Gemara

(Mishnah): Any wood may be used for the Ma'arachah, except for olive-wood or grapevines. They usually used branches of fig, nut and pine trees.

29b (Rav Papa): Olive wood and vines have bumps (they do not burn nicely).

(Rav Acha bar Yakov): Olives and grapes are crucial to Yishuv (the settlement of) Eretz Yisrael, therefore we do not want to cut such trees.

Berachos 50b (Beraisa - R. Eliezer): One may wash his hands with raw wine, but not with wine diluted with water;

Chachamim say, neither may be used to wash.

Shmuel taught that one may use bread for any need. This is like R. Eliezer.

(Beraisa): There are four Halachos about (not ruining) bread: we do not put raw meat over bread; we do not pass a full cup over bread; we do not throw bread; and we do not support a bowl with bread.

Mar Zutra threw some cooked meat (alternatively - dates and pomegranates) in front of Rav Ashi.

Rav Ashi: A Beraisa forbids throwing food!

Mar Zutra: It forbids throwing only bread.

Question (Rav Ashi - Beraisa #1): Just like one may not throw bread, one may not throw (other) foods.

Contradiction (Mar Zutra - Beraisa #2): Even though one may not throw bread, one may throw (other) foods.

Resolution: One may throw only foods that will not get spoiled.

(Beraisa): We may stream wine out of pipes in front of a Chasan and Kalah. We throw parched grain and nuts in front of them in summer, but not in winter (when the ground is muddy). We may not throw rolls in summer or winter.

Rishonim

Rambam (Hilchos Isurei Mizbe'ach 7:3): They would not bring olive wood or vines for the Mizbe'ach, lest it detract from Yishuv Eretz Yisrael. They used to bring fig branches from forests not in settled places...

Be'er Sheva (Tamid 29b DH u'Mihu): The opinion that is not concerned for Yishuv Eretz Yisrael permits even from fertile fig trees. We should forbid due to "Lo Sashchis"! If the tree is worth more than the fruit, why was the other opinion concerned for Yishuv Eretz Yisrael?! Perhaps it is permitted for a great Mitzvah like this.

Question (Mishneh l'Melech): What was his question? One may not cut an entire tree from its roots. For the Mizbe'ach, they cut only branches!

Rambam (Hilchos Shechitah 1:24): One who will slaughter many animals must check the knife after every Shechitah. If he checked only at the end and the knife was found to be Pasul, they are all Safek Neveilos.

Magid Mishneh: The Rambam advises checking after every Shechitah, but one may opt to delay checking until the end. The Rashba calls this improper, lest the knife be found to be Pasul and he transgressed Bal Tashchis.

Rambam (Hilchos Melachim 6:10): Lo Tashchis applies also to one who destructively wastes food. He is lashed only mid'Rabanan.

Rambam (Hilchos Berachos 7:9): One may not put raw meat on bread, or pass a full cup over bread, or use it to support a bowl. We do not throw bread, nor pieces or foods without peels, e.g. strawberries, grapes or figs, because they get spoiled.

Talmidei R. Yonah (on Rif Berachos 37b, DH Ein): One may not put raw meat over bread, for the bread becomes Ma'us (Ma'us). Alternatively, he will need to rinse off the blood stuck on the meat. We do not pass a full cup of wine over bread, lest it spill, and the bread will become Ma'us. Likewise, we do not use it to support a bowl, lest soup spill on it. The Rif brought the Beraisa Stam. It seems that he holds that just like one may not put raw meat over bread or pass a full cup over it, likewise we do not use it to support a bowl. R. Yonah disagrees, for Shmuel permits using bread for one's needs. This is only for this (supporting a bowl). Surely Shmuel agrees about putting meat on it or passing a full cup over it. Soup that falls on bread does not make it as Ma'us as wine that falls on it.

Beis Yosef (DH veha'Rif): The Rif brought the Beraisa of four teachings about bread, and that similarly we do not throw any food that gets ruined. He omitted Shmuel's teaching. R. Yonah connotes that the Rif rules unlike Shmuel. However, the Rashba wrote that it seems that Rav Hai Gaon holds like Tosfos. He said that we do not throw bread or other foods that become Ma'us, but we may throw food will not become Ma'us; also the Rif says so. The Rashba understands that once the Rif wrote that we forbid only what becomes Ma'us, this shows that the Beraisa forbids only such matters. Therefore, he did not need to bring Shmuel's Heter to do all needs with bread. However, why did he attribute to Rav Hai Gaon and the Rif that we forbid only foods that become Ma'us? The Gemara explicitly says so! Perhaps it is because the Amora'im who said so hold like Shmuel, so if the Halachah would not follow Shmuel, it would not follow them. Since the Rif and Rav Hai Gaon hold like these Amora'im, they hold like Shmuel. Alternatively, one might have thought only for other foods it depends on whether they become Ma'us, but one may not throw bread in any case. Rav Hai Gaon and the Rif connote that one may throw even bread if will not become Ma'us.

Rosh (Berachos 7:32): R. Chananel rules like Chachamim who argue with R. Eliezer. Also the Beraisa that forbids supporting a bowl with bread is unlike Shmuel, so the Halachah does not follow Shmuel. However, Beitzah 21b is like Shmuel. Bahag says that we hold like Shmuel only regarding uses that do not ruin the food. It seems that even Shmuel forbids then. The Gemara says that Shmuel holds like R. Eliezer, i.e. R. Eliezer holds like Shmuel, and permits even more, i.e. when the food gets ruined. Therefore, the Halachah follows Shmuel when the food does not get ruined.

Rosh (ibid.): Some eat porridge using bread in place of a spoon, since they eat the bread afterwards. Maseches Sofrim (3:14) says that one may use a food to eat another food only if they are proper to eat, i.e. it is proper to eat them together, and he does so. Do not explain that it permits using foods proper to eat. If so, all the more so one may use foods improper to eat, for they are like wood! If so, one may not use bread to eat porridge (if he does not eat them together). Perhaps Maseches Sofrim is unlike Shmuel, for it forbids using food to support food, and Shmuel permits if it will not become Ma'us. We hold like Shmuel, and use bread to eat porridge. Porridge does not ruin the bread. I saw Gedolim who would eat a little of the bread each time with the porridge. Shmuel agrees with the Beraisa about four laws of bread, except for the Isur to support a bowl with it. We may stream wine out of pipes in front of a Chasan and Kalah if it is caught in a vessel below.

Poskim

Shulchan Aruch (171:1): One may use bread for any need, as long as it will not become Ma'us.

Beis Yosef (DH Amar): Also Tosfos, R. Yonah and the Rashba rule like Shmuel, but only for something that will not become Ma'us. It seems that even Shmuel agrees about something that will become Ma'us, like it says in Shabbos (50b).

Mishnah Berurah (2): All the more so, one may use other foods for all his needs.

Mishnah Berurah (4): For the sake of Refu'ah (a cure), it is permitted even if it will become Ma'us, like we say below (328:20). Even if it is not for Refu'ah, if it is a need of man that is normally done with food, it is permitted. This is why we sprinkle wine on the floor and anoint the body with oil, like the Gemara says in many places.

Shulchan Aruch (ibid.): Therefore, one may not put raw meat over bread, or pass a full cup over it, or use it to support a bowl full of something that would ruin the bread if it falls on it.

Kaf ha'Chayim (2): This is even if the meat was Kashered or roasted.

Mishnah Berurah (5): If the cup is full, it is likely to spill on the bread and it will be Ma'us.

Mishnah Berurah (6): All the more so it is forbidden if the bottom of the bowl is dirty and the bread will become Ma'us.

Mishnah Berurah (7): If the bowl is not full it is permitted. Likewise, one may use bread to cover a Kli.

Kaf ha'Chayim (3): The Bach says that the only concern is lest the bottom of the bowl is wet or dirty. The Acharonim rejected this. One should be concerned for his opinion and check a bowl (that is not full) before supporting it with bread.

Kaf ha'Chayim (4): All the more so, when washing hands before or after the meal one must ensure that the water not fall on bread.

Shulchan Aruch (ibid.): We do not throw bread due to disgrace to food. Similarly, we do not throw food that is ruined through throwing it. One may throw food that is not ruined through throwing it, such as nuts, pomegranates and quinces.

Magen Avraham (1): When one sees food on the ground, he may not leave it. He must pick it up, unless we are concerned for witchcraft, e.g. a full loaf (Eruvin 64b). One may not break olives, even if he intends to sweeten them (Shabbos 50b). The Rif explains that he wants to wash his hands in the juice, and the olives becomes Ma'us. It is forbidden, for one may use Boris (soap). One may not cause food to become Asur b'Hana'ah (YD 350:1). We do not feed human food to animals (Ta'anis 20b). Rashi says that this is due to disgrace to the food. It looks like he rejects the bounty that Hash-m bestowed on the world.

Mishnah Berurah (11): If the place is not clean, one may not throw even nuts, like we say in Sa'if 4. Rav Huna holds that we do not feed human food to animals. The same applies to birds. Eliyahu Rabah is unsure whether the Halachah follows Rav Huna. Machatzis ha'Shekel says that if one has only human food, all permit giving it to animals. Perhaps this is why the custom is to feed bread to fowl.

Kaf ha'Chayim (9): Alternatively, we do not feed human food to animals because the Torah is concerned for the money of Yisrael. This is why Machatzis ha'Shekel permits if one has only human food. The Kesav Sofer (33) says not to feed human food to others' animals, but one may feed his own animals.

Kaf ha'Chayim (7): One should not give any food from the table to a Tamei animal.

Kaf ha'Chayim (10): One may not stick a knife into bread. He makes the bread like a case for the knife.