I think you are right on. If you want to bring your own burger (93% lean) and the 3 bean salad on top of it, do it. I might also bring a "dessert" like Jello or SF candy so you don't feel left out!
Are you on Phase 1 or 2. If on two, there are more options...
Fresh veggies and salsa are one thing I love to munch on at a party when everyone is eating their less healthy 'snacks' like chips, bread, etc. If you're not sure they'll have some, bring some!