Well...
We could do a raffle of donated items from an LFS.
Someone can donate dry goods, a frag pack or a frag of something pretty nice.
Create a list of items needed for the cookout, and volunteers can pick and choose what they will bring. (Burgers, Polishes, Caramel Cake, Forks, Buns, Potato Salad, Steaks, Condiments, Lube, Chips, Sodas, Summer Shandy, Jack Daniels, etc.)
Poker or spades game.
Visit a local LFS as a group prior to the cookout.
Frag Grab Bag. Everyone bring a frag and you get to draw a number and pick a bag with the corresponding number. The more frags you bring, the more numbers you get to draw.
Pajama Party.
I could go on and one....but you get the ideal.