If this is similar to the other thread about nuclear winter then this is more about survival? If it's about survival and only UFC fighters can be picked then the correct answer is Tim Kennedy. Army special forces Green Beret, he's trained for this type of specific situation. They are trained to survive with limited numbers/supplies and are force multipliers, he will know how to recruit and train allies to help you guys survive.
Plus he's a weapons expert and trained for war/combat and probably knows medical information that is related to injuries. Those are skills needed most in those type of situations.