Supply caravans were mentioned, so they can be seen as such, with independant merchants always visiting bases to try and get something.
I plan in adding ina lovely food called a Smirnet. Bland, nutritious, and universally hated by the multitudes of professional soldiers who've had to live of the damn things when they ran out of rations. In a word, they'd by like plump helmets, but unfermentable, and they grow everywhere.
Even urban battlegrounds can have the damned things growing in powered concrete and garbage.