For our engagement party, we said that if people wanted to bring gifts, they could bring a bottle of wine that we could pour at the wedding. I also think this could work really well for beer lovers by having everyone bring a six-pack of beer for the wedding.
I liked this idea because we really didn't need more stuff (we have a small apartment), and it gave some people who probably can't come to the wedding a way to feel like they are a part of it. Also, it's really scalable so people can spend as little or as much as they want.
We also put out shipping tags and encouraged people to sign their names and write messages to us. Everyone seemed to embrace this idea and we received more than two cases of wedding wine.