Gemara

5b (Beraisa - Aba Binyamin): I always exerted myself that My Tefilah should be near my bed.

This means that he would say Keri'as Shema and pray right after rising.

10b (R. Yosi b'Rebbi Chanina): "Lo Sochlu Al ha'Dam" forbids eating (in the morning) before praying for your Dam (life).

(R. Yitzchak): "V'Osi Hishlachta Acharei Gavecha" refers to one who eats before praying;

We read this "Ge'echa." After acting haughtily, you accept Ol Malchus Shamayim?!

28b - Rav Avya: I didn't come to Rav Yosef's class (on Shabbos morning before Musaf) because I was weak.

Abaye: You should have eaten something beforehand!

Rav Avya: Rav Huna forbids eating before praying Musaf!

Abaye: You should have prayed Musaf alone, eaten something, and come to the class!

Eruvin 65a (R. Chanina): Hash-m will shelter from punishments one who is Mafik Magen (he refrains from Magen Avraham, i.e. Tefilah) at a time of pride (when he is drunk) - "Ga'avah Afikei Maginim..."

Rishonim

Rambam (Hilchos Tefilah 6:4): One may not taste anything or do Melachah after dawn until he prays Shacharis. One may taste food or do Melachah before Musaf.

Hagahos Maimoniyos (4): It seems that only intoxicating drinks are forbidden, for we learn from "v'Osi Hishlachta Acharei Gavecha." There is no haughtiness in drinking water. Eruvin 65a connotes like this.

Rambam (7): One may cut his hair or enter a bathhouse close to the time for Shacharis. Chachamim decreed only close to Minchah, for it is common to enter then. Most people go during the day. It is not common to go in the morning. Chachamim did not decree about it.

Rosh (1:7): Aba Binyamin would pray right after rising. He would not work beforehand.

Rosh (10): The Ri says that if one began eating before dawn, once dawn comes he stops. If one began to eat before Minchah, he need not stop. Here is different, for there is an Asmachta from a verse. Avi ha'Ezri permits drinking water before Tefilah. Haughtiness does not apply to water.

Poskim

Shulchan Aruch (OC 89:3): One may not eat or drink in the morning before praying Shemoneh Esre.

Mishnah Berurah (21): One who eats before Tefilah transgresses "V'Osi Hishlachta Acharei Gavecha." Chachamim also made an Asmachta from "Lo Sochlu Al ha'Dam." Even tasting is forbidden.

Bi'ur Halachah (v'Lo): The latter reason forbids even after he said Keri'as Shema and accepted Ol Malchus Shamayim, as long as her did not pray Shemoneh Esre. Therefore, even one who must eat before Tefilah for Refu'ah should say at least Keri'as Shema beforehand.

Kaf ha'Chayim (28): The Zohar connotes that after once slept a fixed sleep on a bed at night, the Neshamah left and only the Nefesh remains, so he may not eat until he prays. This is even if it is before midnight. It is proper not to eat or drink until the end of the Tefilah, i.e. Aleinu.

Shulchan Aruch (ibid.): One may drink water beforehand, whether it is a weekday, Shabbos or Yom Tov.

Beis Yosef (DH u'Mah she'Chasav b'Shem): The Rosh, Mordechai, and Hagahos Maimoniyos citing Sefer ha'Mitzvos wrote that if one is very thirsty, it is better to drink water than to be in pain during his Tefilah. Mahari Avuhav says that this is why we changed the verse. The way the verse is written (Gavecha), we would forbid water, for it is a need of the body. However, since we read Ge'echa, it is permitted, for there is no haughtiness in water. Chachamim were able to change the verse from its connotation, because the Isur to eat and drink before praying is only mid'Rabanan. They decreed only about matters due to haughtiness.

Beis Yosef (DH u'Matzasi): R. Tuvya says that this is only during the week, but on Shabbos and Yom Tov one must bless on a cup of wine before eating, therefore one may not drink (before Tefilah). Orchos Chayim brings this in the name of Tashbatz. I saw a Sefer that permits, because as long as one did not pray, it is not yet time for Kidush.

Bedek ha'Bayis: The Tur wrote that the Rosh did so.

Beis Yosef (DH v'Zeh): It seems that this is primary, especially since some Poskim permit drinking water before Kidush.

Kaf ha'Chayim (35): Since some forbid on Shabbos, it is good to be stringent when possible, even if he is not stringent about drinking water before Tefilah on weekdays.

Mishnah Berurah (22): Water is permitted only without sugar. All the more so beer is forbidden. One may drink coffee or tea before Tefilah in order to help Kavanah, especially where people are used to this and one's mind is not settled without them. The Acharonim permit only without sugar and milk. People are lenient to drink with sugar. Perhaps the Acharonim discuss putting the sugar in the tea to sweeten it. If one puts (e.g. a cube of) sugar in his mouth while drinking, and without this he cannot drink the tea, this is not haughtiness. If he wants to put sugar in the tea, or to eat Targima (Mezonos; some say that this is fruits) while drinking, lest he drink the coffee or tea on an empty stomach, there is no way to permit this, unless he is weak and needs it for Refu'ah. In any case it is good to say first at least Parshas Shema Yisrael. Pischei Teshuvah ha'Chadash says that one should not drink tea with friends before Tefilah. Also, this leads to excess conversation, and sometimes he misses the time for Keri'as Shema and Tefilah.

Kaf ha'Chayim (31): Some permit putting a little sugar in the coffee or tea for one who needs to drink it, for one who cannot drink it without this.

Halichos Shlomo (ha'Gaon R. S. Z. Auerbach, Ztz"l, 2:2): One may put milk and sugar in the coffee. Perhaps one should preface a Tefilah of request.

She'elas Rav (2:6:43, and Ishei Yisrael p.798:45, citing ha'Gaon R. C. Kanievsky Shlita): It is proper to be stringent. Even without milk and sugar, it is good to preface a request

Pninei Tefilah (p.57, citing ha'Gaon R. Y.S. Elyashiv Ztz"l): Anything is permitted if it will help to pray with Kavanah, except for Chemar Medinah, i.e. wine and beer. (It seems that this includes natural orange or grapefruit juice, unless needed for medical reasons - Ha'arah 4.)

Kaf ha'Chayim (34): One who is stringent not to drink even water after dawn will be blessed, for one opinion forbids water. Some say that the Rif and Rambam forbid. One should be stringent, unless he needs to drink to settle his mind, like coffee or tea, or so he will not be in pain during the Tefilah.

Mishnah Berurah (23): Regarding (after Shacharis but) before Musaf, see 286:3 (brought below).

Shulchan Aruch (ibid.): Similarly, food and drink for Refu'ah (a cure) is permitted.

Beis Yosef (DH v'Chasav): Mahari Avuhav says that Avi ha'Ezri would permit eating and drinking before Tefilah for the sake of Refu'ah, for this is not haughty. Kol Bo says that some forbid even water, since his desire is filled with what he needs. Mahari Avuhav brought that Orchos Chayim forbids for the sake of Refu'ah, but he holds like Avi ha'Ezri, and so we hold.

Magen Avraham (12): The Shulchan Aruch connotes that for Refu'ah, one may eat even something to which haughtiness applies, since this is not his intent, rather, for Refu'ah. It is permitted even if he is not sick. The Beis Yosef in the name of Mahari Avuhav connotes like this.

Mishnah Brurah (28): If one must eat before Shacharis, he should eat before dawn.

Kaf ha'Chayim (36): We do not need an expert doctor to permit eating before Tefilah. Even one who is not an expert may permit it.

Bi'ur Halachah (DH v'Chen): The Pri Chodosh and Pri Megadim permit even if he could eat the foods after Tefilah, since he intends for Refu'ah. Chayei Adam says that if one must eat due to weakness, perhaps it is permitted. If one is weak and cannot wait until the Tzibur finishes the Tefilah in the Beis ha'Keneses, he should pray alone in the house and eat a little and afterwards go to the Beis ha'Keneses to hear Kaddish, Borchu and other Devarim shebi'Kedushah. This is better than eating before Tefilah and going to pray with the Tzibur. This is clear from 28b.

Shulchan Aruch (7): One may cut his hair or enter a bathhouse (before Shacharis). Chachamim decreed only close to Minchah, for it is common then.

Gra: The Mishnah (Shabbos 9b) forbids these matters only close to the time for Minchah.

Mishnah Berurah (36): We permit these only close to Shacharis, i.e. before dawn. After dawn they are forbidden. The Pri Megadim forbids entering a tannery or a meal before Shacharis, just like before Minchah. On Erev Shabbos one may buy what is needed for (Shabbos) meals, for this is Shamayim's desire. On a weekday it is forbidden.

Kaf ha'Chayim (52): The Levush explains that Chachamim did not decree about Melachos that are unusual at the time, for he realizes that it is unusual to bathe then, and he will remember (to pray).

Eliyahu Rabah (12): Piskei Tosfos permits (cutting hair and bathing) only before dawn. After dawn, they are no better than other forbidden Melachos. Kol Bo (8b) forbids only other Melachos after dawn. It seems that even a tannery is forbidden. We permit only cutting hair and bathing.

Kaf ha'Chayim (53): One should be stringent, for Eliyahu Rabah (235:6) brought from R. Yerucham that some forbid before Shacharis just like before Ma'ariv.

Halichos Shlomo (2:8(11)). Perhaps one may shower without soap before dawn, or before when he normally prays.

Ashrei ha'Ish (1:19:3, citing ha'Gaon R. Y.S. Elyashiv Ztz"l): One may shower with soap before Tefilah only if he is very sensitive and cannot pray without this.

Shevet ha'Levi (9:1): One may take a brief shower before Tevilah, for this is like preparation for Tevilah (removing Chatzitzos).

She'elas Rav (2:6:46): One may not shower and immerse on Friday morning 'li'Chvod Shabbos' before Shacharis.

Mishnah Berurah (37): Some are stringent about Melachos normally done early, and forbid half an hour before dawn, just like before Minchah. Therefore, it is good to say Berachos beforehand.

Shulchan Aruch (286:3): One may taste before Musaf, i.e. he may eat Peros, or even a small amount of bread, even if it is enough to sustain a person, but a meal is forbidden.

Bi'ur Halachah (289:1 DH Chovas): A sick person who must eat (after dawn) before praying on Shabbos must make Kidush first.

Note: A Moreh Hora'ah told me that we do not follow this Bi'ur Halachah.