With my DD's group of friends we have done
Sloppy Joes
Lasagna
Meatball sandwiches
make your own deli sandwiches
Burgers, hot dogs
Taco's
Pudgie pies they made over the fire
Sloppy Joes are probably easiest and cheapest. I found the tacos were actually rather pricey by the time you buy all the toppings and also time consuming cutting tomatoes and lettuce, etc.
side have been salad, corn on the cob, chips, potato salad, pasta salad, cut up veggies- of course you can figure out which side went with each entree!
Desert can be cookies or brownies, cake, and even frozen stuff like fudge bars or stars from DQ.
This is a group of about 3 guys and 4-5 girls that are seniors.