We used to do week-long potlucks at the school I worked at and everyone would sign up for a different day to participate..

Something I've noticed is that sides & appetizers are the most popular thing that people bring.. I've done it myself- my mom's cheese ball, her potato salad, bacon wrapped walnuts, etc ... Bacon wrapped walnuts are pretty cheap and a mega cinch to make, actually!

For something a little bit more substantial/mini entrees, you could do like turkey & cheese pinwheels- just make wraps with whole wheat flour tortillas and slice them into 2" pieces - some plain, some with mayo, tomato, & lettuce, or make a big batch of chicken salad and take some croissants along for people to slice and make sandwiches with..

I love making soups and things, but I typically keep those out of a potluck equation simply because that would involve bringing in a crock pot to keep it warm- which I don't have (& desperately want) & would be a major pain to cart around, I should think!