A good heuristic, short of trying all combinations of work, shops, and rest and thinking several steps ahead. It would probably be good enough for the simulation.

F / (T + C) still seems arbitrary to me though. Maybe it's F - (T + C) if we can think of T and C in terms of units of food. But for that we'd already need to know the going rate of food.

We can use past values. We can record the amount the worker got paid and the amount of time he spent since decided to work. And we can record the amount of food he got and how much he paid for it all and the time he spent getting there and shopping since the time he decided to get food. Thoughts?

Isn't your F conveying nearly the same information as your C? A shop would nearly always have more than needed for one person. The amount of available money does not change the relation of which shop is selling cheaper. So there remains only the cost.

You did not write about the type of game you are making, is it even necessary for shops to have different prices there?

Wouldn't the simulation get unrealistic, because in reality people do not have perfect information about shops, prices and available goods on the whole world?

Do those people always go to a shop and instantly consume the food, although in reality people buy enough for a week and then just take it out of their fridge?

I think I would simplify it by just letting them go to the nearest shop where they estimate/guess (from historic information, flyers or talking to others maybe?) its not too expensive to buy enough for the week, up to a maximum path length (to not starve on the way). If thats not possible go to cheapest inside that area.

The game is an RTS. The simulation shows what happens if all agents behave in the best way to further their interests, including perfect information. Rather, it's meant to be a sandbox for testing different economic policies. With Internet nowadays most information is available. The workers buy a supply that lasts them for a while. If I simulated information dissemation between workers, on what condition would two workers share their information? Then if a corporation decides to lower prices they can pay to post ads on other buildings.

If I don't include the amount of food that is to obtained at a shop in the formula, the cost might be for a single unit of food,

1 / ( T + C )

Then time (measured in terms of money) overshadows cost.