I think coins of various metals sounds good, maybe a barter system too. Maybe it can vary from town to town depending on what they want.
"We're running low on smokes, that's a problem." Said Milton as he jumped out of the bed of the truck, his knees bending only slightly as he landed. Sand kicked into the air and soon dissipated. For some reason it reminded him of the situation they were all in. Just sand. More and more sand, everywhere they went. The people were sandy, the cars were sandy, the houses, the food, the water. Sometimes he wondered if that's why he liked flames so much. He was a crusader in his head, washing away all the sandy, dirty bullshit that the last generations left behind.
He removed his skullcap revealing his messy unkept mop of an excuse for hair, wiped the sweat from his brow and sighed. He then reached into his hoody pocket and pulled out another cigarette and his favorite zippo lighter.
"So...we've got the money right? and we've got the mercury. So that asshole in their is no longer involved in this little equation of ours. Why don't we do a little smash'n'grab before we go?" Milton said with a cocky grin.