Yes, as long as you consume them before or during the trip. Customs regulations of a given country may prohibit the transport of certain goods, e.g. meat, milk, seeds, etc., both in hand luggage and in checked baggage. Also remember that any liquids, gels, cosmetics with a packaging capacity of more than 100 ml. will have to be removed at security checks if you are carrying them in your hand luggage. A passenger traveling with an infant may obtain permission from the security control employee to transport more milk for the child's needs. Consuming drinks bought in the duty-free zone or prepared by yourself sandwiches on board the plane is allowed, but not in a good tone ;)