for me, it's easy to make a couple of different pasta salad combinations. bags of pasta are pretty cheap. i like rotelli pasta with cubed red/yellow/ or orange bell peppers, chopped up carrots, red onions celery, artichoke hearts, olives, etc and a part of a bottle of italian dressing. you can add cheese or not, no cheese would be better if it's sitting outside. another easy one is a penne with fresh chopped italian basil, cherry/grape tomato, mozzerella balls, in a wine vinegar/oil dressing. All of these can be made the night before and they taste better the longer it marinates. one dip is not to add tomato or cheese until the day of, the dressing can make it mushy.
a veggie plate (much cheaper to assemble one yourself) with baby carrots, sugar snap peas, grape tomatos, cauliflower/broccoli, and instead of a traditional ranch type dip, use hummus. Trader joes has a great white bean hummus dip. can also have a bag of pita chips to dip into the hummus too.
bruschetta is nice too. chopped up tomato, fresh basil, a little garlic, good balsamic vinegar, olive oil. serve with sliced baguette