I was wondering on the following halacha.
If one eats an appetizer in a restaurant before washing for the main meal (say for example they eat some vegetables and have some water), do they have to be concerned about making a bracha achrona?
Also, say for example on Shabbos one has heard kiddish in shul and then goes to eat their meal and before they wash they have something to eat/drink. Again should one be concerned about a bracha achrona?
In principle the answer to this is that yes, one must be concerned for the beracha acharona, depending on the foods that are eaten.
This is because in most cases, food eaten before a meal does not have a connection to the meal itself, and therefore the final Birkas Hamazon after the meal does not “cover” the food that was eaten before the meal.
However, if one eats something during the meal that one would need to recite a beracha on even during the meal, and one has intention to eat of this food during the meal, no beracha acharona is made before the meal. Because the person will be eating of this food during the meal, and the beracha rishona was required for the food eaten in the meal, the final Birkas Hamazon is effective for this food.
The same idea applies to an appetizer: If the food is meant to whet the appetite in preparation for the meal, the food is connected with the meal, so that the final Birkas Hamazon is effective, and one should not make a separate beracha acharona.
To sum up, concerning foods eaten before the meal:
1. If one eats something that a beracha would not be made on during the meal, such as a big of potato kugel, a beracha acharona must be made.
2. If one eats something that a beracha would be made on during the meal, such as a fruit, no beracha acharona is made.
3. If one eats an appetizer no beracha acharona is made.
4. Mezonos such as cake or cookies involves something of a doubt (whether a beracha is made on them during the meal or not), and the Mishnah Berurah recommends not making a beracha acharonah, and having explicit intent at Birkas Hamazon that the cake should be included.
See Mishnah Berurah 176.