Our guild also does a fabric challenge. We each receive the same charm pack. We then have to make a wallhanging with the charm pack and a couple of other fabrics of our own. We have certain sizes that it can not go over but your guild could come up with their own guidelines.
The ugly fabric challenges are fun also. You may want to think of a few small challenges for occasions through out the year, like Valentines Day, Easter, ST. Patties Day, etc. You could even do pincushion challenges with a theme. Just have fun with it.