I am totally in favour of a limited implicit food supply for troops, and basing it on the regions they've been through recently is totally reasonable.
I would add diplomacy into the mix - in foreign or hostile lands, resupply should be quite slow, in friendly lands it should be fast.
And "implicit" doesn't mean that it is hidden, I'm all for showing it, not the actual number but something like "supplies will last for est. x days".
Then maybe later we can add options for players to influence it, e.g. explicitly buy food, but at the start it should be really simple and automatic.
