hi, I always like to take something that I don't have to cook and can throw together fast. One that is always popular is greek salad. I bring all the ingredients and a big bowl. chop and toss just before the potluck and you're done.
I use a red onion, cherry tomatoes and a jar of pitted black olives, green & red peppers ( notice that none of the above ingredients require refrigerating ? ) and a cucumber. I bring along greek seasoning, olive oil and some red wine vinegar to toss on it. The only ingredient that does need to be in a cooler is the feta cheese. Cheers !