My aunt has thrown some bridal and baby showers with 80+ guests. This is one of the games she uses.
Upon arriving, each guest is asked to write her complete mailing address on the front of an envelope. All the envelopes are put in a basket. Whenever the gift opening part of the shower seems to have gone on for a while without a break she declares, OK, everybody, its time for a prize drawing. At this point the bride reaches into the basket and pulls out one of the envelopes. The guest whose envelope it is wins a prize.
Personally, I dont like this game. Why? Because the envelopes will be turned over to the bride at the end. They are the envelopes for her thank you notes!
I just think its really tacky to dupe the guests into addressing their own thank you notes. In fact, when Aunty did this game for my (surprise) bridal and baby showers, I made a point not to use those envelopes for my thank yous. I wrote my own.