In the game's current state there isn't really anything to do but PvP so that's what I do. Usually with a group or with friends. When they add lots of zombies things are going to be much much different though. Rather than simply going door to door in cities and getting all the food you need you'll always be chased by zombies or have to sneak by them because they would be everywhere. Camping, hunting, base building, and storage for gear will also give tons more incentive to PvE. But for now I have to kill.