I will identify two memories that I think are the most important that the Giver imparts to Jonas. They are the memory of the war and the memory of the Christmas scene.
These two memories give Jonas a really good idea as to both the good and the bad of what can happen in a society that is less controlled than the one he lives in. He sees the good of his society -- it prevents the tremendous pain and suffering that happens in war. But he also sees the downside of his society. He sees how happy people can become when they have families and love as in the Christmas memory.
These two memories, then, give him a pretty balanced view of what life in a different kind of society would be like.