I would miss books and imagination. Everything in The Giver is tightly controlled. Everything is practical. There are no stories, and no sense of wonder. As an English teacher, I cannot imagine a world without storytelling. It robs us of our humanity.
There is no sense of individuality in The Giver; life is patterned and feelings are dictated. Everyone has to be kind and accepting all the time and confess any of their negative feelings. There is no opportunity for personal expansion if one cannot entertain human emotions. No growth can come in a person's psyche and soul if he/she is not allowed to truly feel negatively and positively.
That loss of identity seems to be the greatest loss in distopian books like these. If you readA Brave New World,Anthem,or1984, Identity and free choice are the main things that are missing; and, there always seems to be someone in the story who questions the society and either revolts and escapes or is brainwashed into the society eventually. For young adult literature that shows distopias, check outUglies, Pretties,andSpecials. This series has a lot of action- and technology-packed scenes dealing with the same issues that seem to be in all distopian stories, only this one is more up to date than those listed above.
So you're asking about material things that we would miss? I think post 2's response is right on target. I would miss love and romance and individuality - the freedom to be unique, my own person with my particular set of likes and dislikes and the personal freedom to decide what to do.
For me, the main thing would be love and romance and everything that goes with that. I would hate not being able to feel love the way I can in this world with my wife and children. This would surely be the worst thing (assuming I could remember that I used to have those feelings).