I’ve ordered platters from local deli.
We also order local ethnic takeout food from delis–Korean, Thai, Italian, Japanese–whatever is desired. Most places are happy to accept your catering order and many will deliver if you’re over a certain minimum total order price. Some deliver in coolers, so the food is piping hot.
I am surprised that college kids love the cheese rolled in salami/ prosciutto that is available at costco ( in the chill cabinet near cheese items) My girls always request for parties. We grilled some of costcos fresh chicken wings and they were a huge hit. ( though maybe messy for a nice party)
Amazon wants to go B&M?
Makes sense since CostCo is trying to go Amazon. 
I recently attended an event that had sandwiches from Costco. They looked like croissants cut in half, with meat and cheese inside and there were a couple of cups of condiments included in the middle. I didn’t have one, but they were gone in no time. Everyone said they were very good.
I’ve had good luck bringing devilled eggs to potlucks (never any leftovers to bring hoem), but perhaps one of your guests will bring that. Another thing that has worked well is pigs-in-a-blanket. I got them frozen, Hebrew National brand, at Costco. I susepct that Sam’s has the too.