Have you ever played the game file? It's about how gasoline admituons have made the ozone so bad in places that they are uninhabital, and how vehicles that use gas are banned by government, well these illegal street racers trade FUEL! or GASOLINE!! so there for the best way to survive the zombie apocolips would be to trade and barter. Say you can trade something for someone to let you tag along on the ride for a few miles. Not only will it make travel easier nd faster, but you may also be able to form a alliance; bit be carefully you don't want to hve a large group following you because that makes you a vulnerable target. Not to mention he problems that would arise within the group it's self. Someone may accuse another person of stealing something or something of that matter And next thing you know there maybe bullets flying in every direction and not for the good reason of warding off a zombie attack, not to mention that all that noise would than attract all the zombies within a 3 mile radius or more
I doubt that there will ever be an issue of something to trade/barter. I suppose the problem will be finding someone who won't kill you (or tie you to a post..naked..like a human pig roast for the undead), and steal your stuff.