12 for grilled dinner Saturday night.
In addition to whatever meat you decide on, grilled vegetables. They're great and very easy - can easily be prepped the night before or even earlier than that. Chunk cut whatever vegetables you'd like, drizzle with olive oil, salt pepper, crushed rosemary (or whatever) and toss. Bell peppers, red onion, carrots, summer squash, zucchini, mushrooms, baby new potatoes, and as boyzoma recommended to me, cherry tomatoes toward the end of cook time. You could also add corn on the cob but cut into about 1-1/2 earlets.
Make a double thickness "basket" of heavy duty aluminum foil. Punch holes to let moisture out/smoke in. Place on hot grill and dump in vegetables. If you have potatoes, I'd start them by themselves for about a 10 minute head start. Personally, for 12 and if you've never done it before, I'd take the easy way out and omit potatoes. Stir around about every 5-ish minutes till vegetables are crisp-tender - about 20 minutes or until your desired doneness is reached.
Big sides of salmon are easy to prepare if your grill is big enough and they're VERY quick. I agree that prepping veggies and sides on Friday is going to be the key. That would be good with asparagus and a made-ahead quinoa or bulgur salad.
London broil or flank steak is another good idea -- I definitely think a big piece of whatever meat/fish you're planning will be much easier than a dozen burgers or chicken breasts.
If you want to go in the red meat direction, you could do a southwest marinade for the London broil, and serve with tortillas and grilled peppers/onions, salsa, guacamole, and sour cream. Add some grilled corn and/or mixed veggies, a big pitcher of margaritas, a big leafy salad with a lime-ish vinaigrette and you've got a party.
1. Marinate a London Broil on Friday night, prep some veggies (peppers, onions, mushrooms, etc.) and get some fingerling potatoes to roast.
2. Crock pot some pulled pork, then put it in a pan on the grill Saturday. On Friday, make a slaw. Use some slider buns. Grill Corn on the cob, if it is available in your area. If not, it's a good time of year for grilled asparagus. A potato salad and/or pasta salad would be great as well.
Enjoy and have fun.