Brachot on Food One Eats Before a Meal
If one eats before a meal in a number of cases one is exempt from making a Bracha Achrona because it is exempted by the Birkat HaMazon after the meal. In other cases, though, the foods are not exempted and require a Bracha Achrona as usual. Lastly, in the cases where there is a dispute as regards to the halacha, one should be strict to avoid that situation. See further for details.
Exempting Other Foods
- If someone is eating foods before a meal and the same food in the meal he should have in mind that the food before the meal is going to exempt the food during the meal. Consequently, the food before the meal is connected to the meal and birkat hamazon will cover it, therefore it doesn't need a bracha achrona.
- If someone is eating food before a meal to whet his appetite many poskim hold that the birkat hamazon covers those foods even prior to the meal and as such one should not recite a bracha achrona. However, since this is a dispute one should avoid eating more than a kezayit before the meal. Examples of this include wine, liquor, or salty foods before a meal. This exemption only works if one eats these foods immediately before the meal, such as within fifteen minutes.
- If one drinks a drink before a meal one should not make a bracha achrona if one is going to drink during the meal. If one is not going to drink during the meal one should recite a bracha achrona. However, wine and liquor whet a person's appetite and don't require a bracha achrona before the meal.
- If a person drinks wine before a meal one should not make a Al Hagefen afterwards. However, because there is a dispute whether the wine is exempted by the Birkat HaMazon it is proper to avoid this situation by either by drinking a melo lugmav and not a reviyit, having intent when saying Birkat HaMazon that it should cover the wine, or have intent that one's Hagefen upon the wine before the meal should exempt the wine that one drinks in the middle of the middle as long as one does have wine in middle of the meal. 
- Regarding Kiddush, according to Ashkenazim it's preferable to drink a Melo Lugmav and not a Reviyit. According to Sephardim, it's preferable to drink a Reviyit and have intent that the Birkat HaMazon should exempt the wine.
- Mishna Brurah 176:2:1, Vezot Habracha (p. 80). Igrot Moshe 3:33 elaborates that the food before the meal exempts the food in the meal even though one actually intended to eat that food and enjoy it as long as one also had intent to exempt the food in the meal since it is then connected to the meal. See Talk page that in fact this ruling of the Mishna Brurah follows the Tosfot, Rosh, Baal Hameor, Shulchan Aruch, and Magen Avraham, but the Ramban holds that a bracha achrona should be made even if the food would have exempted foods in the meal.
- Mishna Brurah 176:2:3
- Shaar Hatziyun 176:9
- Mishna Brurah 176:2:3, Vezot Habracha (p. 81)
- Mishna Brurah 174:24
- Vezot Habracha (p. 81)
- Mishna Brurah 174:25, Vezot Habracha (p. 82). The Magen Avraham 174:14 writes that according to those who require a bracha rishona on drinks in a meal the drink before the meal is coming to exempt the bracha of the drinks in the meal and as such doesn't require a bracha achrona. Additionally, according to the Baal Hameor for any drink that one continues to drink in the meal it would not require a bracha achrona since it is considered like one long drinking. Vezot Habracha proves from the Shaar Hatziyun 174:38 that the main reason to accept the Magen Avraham is the first reason and not the second one.
- Biur Halacha 174:6 s.v. v'afilu
- Vezot HaBracha (chap 9, p. 84) writes that because drinking wine before a meal involves a dispute one shouldn't make a brahca achrona. However, he quotes three advises from the poskim to avoid this situation. The first is to drink less than a reviyit in order not to become obligated in a bracha achrona. The next is to have in mind when making the Birkat HaMazon that it should exempt the wine one drank before the meal. Lastly, he advises that if one will drink wine in the middle of the meal that one has intent that the hagefen before the meal will exempt the wine in the meal.
- Beiur Halacha 174:6 s.v. Vechen, Vezot HaBracha (chap 8, p 84)
- Or Letzion (vol 2, 20:22)