Do foods before a meal require a bracha achrona?
* The Rashba (Brachot 41b) ponders whether any food eaten before the meal is considered disconnected from the meal and requires a bracha achrona or perhaps since
after the meal anyway you are going to recite birkat hamazon there is no reason to recite a bracha achrona now. He quotes a Yerushalmi which seems to dispute this exact point. His conclusion is that one should make a bracha on all food before a meal since they aren't connected to the meal. This is also the opinion of the Ramban (Milchamot Pesachim 24a).
* However, the Baal Hameor suggests that there is a major exception to this rule. Anything which requires a mein shalosh should be exempted with the birkat hamazon and as such does not require a bracha achrona before the meal. The Raavad, Ramban, and Ran explicitly disagree with such an idea and prove from Brachot 41b that it is indeed incorrect. As is evident from the discussion of the Baal Hameor himself the Rif disagrees with his idea as well.
* However, the Rashba (Teshuva 1:72) agrees with the Baal Hameor but limits it to wine and dates. He writes that wine and dates are filling foods (Brachot 13a, 35b). However, for everything else that requires a mein shalosh the birkat hamazon will not cover it as the Ramban proved.
==Connection to the Meal by Exempting Other Foods==
* Tosfot (Pesachim 100b s.v. yedey) writes explicitly that wine coming to exempt other wine in the meal doesn't require a bracha achrona. The Magen Avraham 299:11, Pri Megadim E"A 299:11, and Mishna Brurah 299:27 explain this concept simply. Since the wine before the meal exempts the wine during the meal and the wine during the meal is exempted from a bracha achrona as it is covered by the birkat hamazon, the wine before the meal is also exempted by the birkat hamazon and considered one long drinking. This approach is similarly adopted by the Tosfot (Brachot 41b), Rosh (Pesachim 10:4), Tur 299:8, Baal Hameor (Pesachim 24b), and Gra 299:8 and codified by the Shulchan Aruch 299:8.
* However, the Nishmat Avraham argues that maybe the baal hameor only said it about wine since birkat hamazon could cover al ha’gefen but not for shehakol. The Shulchan Aruch Harav and Mishna Brurah argue on the Magen Avraham and say for drinks before the meal that you’re going to continue to have in the meal you should make a bracha achrona before the meal. The Chachmat Adam writes a safek whether we hold like the Magen Avraham. Rav Ovadia accepted this Magen Avraham at least for a safek brachot, but the Ish Matzliach on Mishna Brurah argues with Rav Ovadia since we pasken like the rosh in pesachim and so it only helps to have wine which increases your appetite but not other foods.
==Connection to the Meal by Whetting one's Appetite==
* The Rosh (Pesachim 10:24) writes that the reason that there's no bracha achrona on the first two cups of wine at the seder is because they are like appetizers which whet one's appetite for the meal. This is accepted in Shulchan Aruch 174:6, Magen Avraham 174:9 and 299:11, and Mishna Brurah 174:24.