People who live around here: think of what you want to make/bring: salads, potato salad, beans, desserts, etc. If you have a large cooler, that would probably be helpful to hold cold drinks. If you have any long folding tables, we could use those too, as well as newspapers to spread out on the tables for the mudbugs.
People from out of town: think about bringing drinks, rolls, plates, napkins, cutlery, a package of hot dogs and buns, chips, salsa, ice, paper towels, plastic cups, etc. There are several grocery stores in Elsewhere's neighborhood.
When in doubt bring beer or wine or soda.
Never can go wrong with drinks.