Perhaps each settlement could be specialized in a certain type of produce because of geographical differences (fish near the river, cattle on the countryside, and other man-made goods, scraps, and so on), and they trade between each other, without needing any kind of coin. 
And yes, meals and a place to live in exchange for work sounds the most plausible.

I'm also curious about the Roaches:
- Are they nomads, or have they found a hideout and live in an occupied settlement?
- Have they ever attacked a settlement, or do they just watch the roads?
- Are there various clans within the Roaches, perhaps in conflict with each other (like an organized crime group)?