They don't anymore, the calendar produces enough money to purchase gift certificates from the sponsors.
So you can pick the sponsor you like or is close and buy what you want.
We found this solved a whole host of problems. #1 everyone wins
Sponsors get back from the club, members can use the certificate towards something they really want. It has allowed us to run the contest every month since we started running it with calendar funding without having any issues with where the prizes would come from.
When I started some of the prizes where donated from members.