Several ideas already given that we usually do around here too. I like the idea of asking the guests beforehand to bring a non-perishable food item that starts with the beginning of their name. These are all collected in a laundry basket (who can't always use those?) and given to the bride-to-be. The item is announced when you go around introducing yourself at the beginning of the party. Sally brings soup, Patty brings a box of pasta, etc.
We also ask the guests to bring a recipe card with their favorite recipe, and they collected and put in a gift of a recipe card box.
Clothespin goes on the pants legs or sleeve of each guest. When a person is caught crossing their legs, that person who catches them takes the clothespins. Whoever has most wins.