If I were cooking for that many and only had a cast iron grate, I would go with a combo of pork tenderloin “steaks” that I cut from the cheap $20 whole tenderloins at Costco, boneless but skin on chicken thighs and some cheap hamburgers done smashburger style.
For the chicken I would probably buy two BBQ sauces, such as the Big Bob Gibson white sauce that goes amazingly well on chicken and the savory and slightly mustardy flavor of Blue Front BBQ sauce. For the pork tenderloin steaks I would do half in the same Blue Front BBQ sauce as it’s the only commercial one I think that works well on all bbq meats from turkey to shrimp to beef. The other half of the pork tenderloin steaks I’d use Banchan’s yuzu flavored Japanese bbq sauce. For the burgers I’d either have standard ketchup, yellow mustard, and mayo or bring along some Peter Luger’s steak sauce or HP along with Grey Poupon Dijon mustard if I wanted to be a fancy lad.
These are for reference only as they are cheaper elsewhere.