For a "I don't have anything planned but the boys are coming over" game, I always fall back on Ganesha Games product, especially "Mutants and Deathray Guns". I usually just throw out a scenario. In this case, find the drinkable water source. I have cards made up for all the figures, so we just randomly deal each player 5, and make sure one has the "Leader" skill. So, with that said:
Somewhere in the Null zone, at the scene of an ancient battle between Giants, a source of untainted water springs. Five desperate factions fight for control...
Rombo and other members of the gang take cover behind a destroyed Giant Robot.
Mutants take the high ground.
Squilliam the Psychic
The battle rages.
In the end, it was called because of time. We could have finished quicker, but it was one of those nights where we spent alot of time BS-ing. The figures are mostly old GW stuff, repurposed for the dark future. I have more of a Kamandi / Gamma World / Thundarr take on the post apocolyptic theme. So the minis are painted in more of a comic style (bright colors) than a dark. dirty realistic vein.
The destroyed bots are old bases for Marvel action figures.