30th B-Day

I`m planning a party for my husband`s 30th B-day. I plan to have it at our home and wanted to do something fun, but need some ideas. A friend suggested asking guest to bring 30 of the same item as a gift, but how do you ask for gifts to a party, isn`t that rude? It could be funny, like 30 Asprins or his favorite idea is 30 BUCKS LOL :) Any help on the wordage of this, would be great.