Gemara

41a (Beraisa): If one wants to eat a radish and an olive, he blesses on the radish, and exempts the olive.

The case is, the radish is primary. (He eats the olive just to weaken the sharpness of the radish.)

43a (R. Zeira citing Rava bar Yirmeyah): We may bless on incense from when the cloud of smoke arises.

Question (R. Zeira): He does not smell it yet!

Answer: (Rava bar Yirmeyah): One blesses ha'Motzi before eating the bread, because he intends [and is about] to eat. Here also, he intends [and is about] to smell!

44a (Mishnah): If one was served first salted food, and bread with it, he blesses on the salted food and exempts the bread, for it is Tefel to it.

Rishonim

Rosh (6:26): Do not say that the radish exempts the olive only when one eats them together. The Gemara connotes unlike this. Rather, he ate one after the other, to nullify the bitterness of the radish.

Terumas ha'Deshen (31): If one does not want to drink on an empty stomach, and they bring him a seasoned or sharp food beforehand, to sweeten the drink, must he bless on it? This is just like blessing on the radish to exempt the olive. The Rosh says that we do not discuss [only] when he eats them together, rather, even when he eats them one after the other. Here also, one blesses on the drink and exempts the food. However, there first he eats the Ikar and blesses on it. Here he eats the Tefel first. How can the Berachah of the Ikar afterwards retroactively exempt the Tefel? He already benefited without a Berachah! However, the Or Zaru'a says that one who eats cherry pits in order to sweeten the drink does not bless Borei Peri ha'Etz on them, like we bless on all [sweet] pits of fruits (202:3). Rather, he blesses sheha'Kol, since they are only to sweeten the drink. If so, here one blesses sheha'Kol on the food, even if normally it has another Berachah. We do not distinguish between foods and drinks. The Gemara asked that bread should exempt also wine! Rather, Chachamim never enacted to bless on any eating or drinking that is Tefel.

Beis Yosef (OC 212 DH Kasuv bi'Terumas): The Tur (Sof Siman 210, in the name of the Rosh) said that the Shi'ur cannot change the Berachah. It seems that likewise, just because it comes to sweeten the drink does not change the Berachah.

Poskim

Shulchan Aruch (OC 212:1): One blesses on the Ikar, and this exempts the Tefel. This is not only if the Tefel is mixed with the Ikar. It is even if each is separate.

Rema: One blesses on the Ikar and exempts the Tefel when he eats them together, or if he eats the Ikar first.

Taz (6): We find (43a) that one blesses on incense once the smoke goes up, even before he smelled it, since he intends to smell it afterwards. Also here, we can say that since he intends to drink wine and eat first, he may bless immediately on the wine, eat the pit, and drink! Do not say that this would be a Hefsek (interruption) between the Berachah and drinking. Regarding ha'Motzi, speaking between the Berachah and eating is a Hefsek, and even so, if one said 'bring salt or an accompaniment (for the bread)', it is not a Hefsek, since it is needed for the eating. Here also, the eating is a need of the drinking! I answer that here it is a different benefit than the drinking, therefore it is a Hefsek.

Gra (DH Techilah): The Mishnah said that he was served first salted food (the Ikar). The Tosfos Yom Tov says so. However, he rejected this proof. Perhaps it teaches that even though he does not eat them together (the Ikar exempts the Tefel). This is like Tosfos, who says that he eats the bread afterwards. However, R. Yonah says that he eats the salted food with bread.

Damesek Eliezer: The Gra asks that according to R. Yonah, if he eats the bread before or after the salted food, he must bless on it. Therefore, it is difficult why the Mishnah says that he ate the salted food first. I say that R. Yonah said only regarding bread that it is Tefel only if he eats it with the Ikar. Regarding other things, he agrees that it is Tefel even if he eats it afterwards.

Rema (ibid.): If he eats the Tefel first, e.g. he wants to drink, and he eats first so that he will not drink on an empty stomach, or he eats cherry pits to sweeten the drinking, he blesses on it only sheha'Kol, since it is Tefel to something else.

Taz (7): The Rema disagrees, and wrote (Darchei Moshe 2) 'I disagree. Since it (the pit) is Tefel to something else, the primary Hana'ah is not from it, so it does not get its normal Berachah. However, one must bless on it to avoid benefit from the world without a Berachah. One is Yotzei through sheha'Kol. This is unlike less than a Shi'ur. There, he gets the primary Hana'ah, and must say the proper Berachah.' This does not refute the Beis Yosef. Also less than a Shi'ur is not the primary Hana'ah. This is like Tefel! Both are partial Hana'ah. The Levush says 'the Rosh says that for a incomplete Shi'ur, there is no reason to change the Berachah, but (perhaps) one does not bless at all. Here, surely one must bless, but one can exempt it through the Ikar. Since one may not benefit from this world without a Berachah, and he already benefits before eating the Ikar, one must bless first, but not for it (the Tefel) itself, rather, for the Ikar that he wants to eat afterwards. The Rosh would admit that the Berachah changes!' I disagree. Also regarding a partial Shi'ur, we should say that he should bless Borei Nefashos, lest he benefit from the world without a Berachah! Even so, the Rosh says that Borei Nefashos does not apply to something whose Berachah is me'Ein Shalosh, even for less than a Shi'ur. I would answer differently. There we discuss a Berachah Acharonah. We do not have a general Berachah Acharonah. Every species has its special Berachah Acharonah. Therefore, one may not change. Regarding a Berachah Rishonah, there is a general rule. One who said sheha'Kol on anything was Yotzei, but due to the importance of some species, l'Chatchilah one must say their special Berachah. Therefore, whenever the special Berachah does not apply, for he relies on the Ikar, we apply the general rule, and he blesses sheha'Kol, for also this is its Berachah.

Magen Avraham (4): I say that the Or Zaru'a holds that one blesses sheha'Kol only when it is Tefel to other drinks. It would be proper to bless sheha'Kol on the drink to exempt the pits, but since he eats the Tefel first, he must bless on it. Therefore, he blesses the Berachah of the Ikar. When the Ikar has a different Berachah, he does not bless sheha'Kol on the Tefel. However, Terumas ha'Deshen understands that the Or Zaru'a holds that even if he drinks wine, he blesses sheha'Kol on the pits. Since they are Tefel, they lost their Berachah. Afterwards, he blesses Borei Peri ha'Gafen on the wine. What is the source for this? Also the Beis Yosef disagrees. Therefore I say that one should not rely on this. See what I wrote in 174:7 (brought below).

Gra (DH Aval): This (the Rema's law) is astounding. Also the Magen Avraham disagreed. See the Taz.

Mishnah Berurah (10): L'Chatchilah, one should avoid eating the Tefel before the Ikar.

Kaf ha'Chayim (11): The Pri Chodosh and Magen Avraham agree with the Mechaber, that one says the usual Berachah. The Taz agrees with the Rema. Eliyahu Rabah says that all Acharonim say so, and this is primary. The Acharonim say that to avoid the Safek, he should first drink some of the Ikar, and bless with intent to exempt the Tefel.

Bi'ur Halachah (DH v'Eino): Perhaps the Rema's law is based on what he wrote in 204:11 from the Ro'oh, that we bless sheha'Kol on a jam that healthy people do not normally eat. Since it is only for Refu'ah, its normal Berachah does not apply. Even though he does not intend to benefit, he benefits, therefore he blesses sheha'Kol. The same applies here. However, one could distinguish. There it loses its Berachah because healthy people do not eat it at all. Here, healthy people eat it, just he ate it like a Tefel. Perhaps it keeps its Berachah. Even there, the Acharonim rule unlike the Ro'oh, so all the more so here he blesses the usual Berachah.

Shulchan Aruch (174:7): One does not bless on water or any drink other than wine during a meal. It is considered due to the meal, for it is not normal to eat without drinking. Even if he was thirsty before the meal, since he did not want to drink then lest it harm him, he drinks due to the bread, so bread exempts it.

Magen Avraham (12): This is only if he eats a fixed meal. If he has only a little bread, see Siman 212.