Though it seems to buck the norm, I typically stay away from grilling meats for larger groups, as I find it to be a time-intensive and time-dependent activity. It can end up being you (or another) stuck at the grill flipping burger after burger, and then you factor in the timing of the done-ness....well, it can get tricky. Plus, if it were to rain, transferring a grill-plan for a larger group to a cooking-in-the-kitchen plan can be logistically difficult. So I usually go with a crock pot (or two) of something or another (a beef roast with red wine poured over and spices of your choice, then pulled apart or sliced, is delish on buns with fixings if you desire), along with a baked pasta dish, as my main offerings, and then have various sides (I second the bean salad idea, and corn on the cob always goes over well, with butter, spices, and Parmesan cheese to top it if desired). I always have veggies, fruit, chips, cheese, etc. out (simple stuff) for constant noshing opportunities, and this also helps with picky kids....there's always at least something they'll be happy with. I'm also not much of a dessert person (or baker), but I know others love the sweets, and have found that sliced pound cake with fruit, whipped cream, and chocolate sauce for people to add to it is always a hit.
On keeping drinks cold, we go with a couple of coolers, one with nonalcoholic, one with. I always have several ice bags (and refills) standing by and try to keep them relatively full. I usually have throw away cups with a permanent marker handy (but high enough that the little ones can't get to it) for people to mark their drinks.
Add some badminton, a bags tournament, and some music and we're good to go! Have fun!