Hullo!
In this guild I was in on American WoW, every week they made an Optional Lottery, on every Monday, each person (if the wanted to particpate) would send 10s to the Guild Master and a number between 1-100, and the Guild Master would already have picked a number.
The person with the closest number to the Guild Master wins all the money sent by the members.
Since our guild is relatively new, we should make it I think 5s, but it's your choice I guess.