After everything that has happened, Mordecai needs a lot of drinks and wants you to blast the kegs off of a Hodunks booze runner van in The Dust. Fast travel there and grab a vehicle, then go chasing after the booze runner, which is marked on your map. It does move pretty fast, but your vehicle is definitely faster than it is, so you should have no trouble keeping up with it when you need to do so.

View Full-size

You need to shoot the barrels on the truck in order to get them to drop.

The slight catch with this mission is that shooting the actual van does nothing, as the kegs will not fall off of it. Instead, you need to actually aim at the kegs sitting on the van themselves. After knocking off five barrels, Moxxi will chime in and offer you a reward if you bring the booze to her. Her reward is a pistol named Rubi, while Mordecai’s is a sniper rifle called Sloth. Once you get the ten barrels, bring them to whoever you want.