Han Solo, Chewie, Luke and Leia vs Mal, Zoe, Jayne and Inara.
They get equivalent firearms, no other weaponry or equipment.
Rumble takes place in a large, 20th century shopping mall with two stories (there's a balcony along the 2nd that let's you see the first floor). They start at opposite ends on the second floor and cannot see each other at the start due to distance, angles, curvature, department store displays, etc, so at least one group must advance forward to encounter the other.
Star Wars characters from just after blowing up the Death Star, so Luke has not trained with Yoda yet.
Firefly characters from just after the first season.