Whenever I look at the price lists of Mutant Future ™, it reminds me of how much of it was really just taken straight from Labyrinth Lord ™. For example, the barter goods table states that a pound of wheat is worth about one copper piece (cp), which is the smallest coin in the game system. A nice price in a pseudo-medieval fantasy world where agriculture is practiced on large fields… but for a weird-science-fantasy post-apocalypse…?
If I think about a “weird apocalypse”, I see civilization in ruins, mutation abound, contamination and a struggle for survival. For survival to be at risk, one of two things are typically true: there is a threat (or: multiple threats) that actively ends the life prematurely (plagues, monsters, freak weather, marauders) or the very basics of human survival are not covered. Those basics are water, food and shelter (perhaps not EXACTLY in that order). Of course, one can rule that food and water simply aren´t the problem, that (mutated) humanity is about to recover and that the small villages start to turn into towns once more, with this prosperity being the cause for people heading out to explore the world. After all, it is not like gathering (or: planting) food is the first issue of every day anymore. It -is- a valid approach, let me stress this, but in my opinion every post-a-setting benefits from food being a little scarce. Why? Well…
1) It sets the tone
If the players keep track off their provisions as much as they keep track of their gold pieces, ammo and hit points it drives home the struggle of survival, and does so without them ever actually having to deal with any in-game mechanic for starvation EVER! Especially a hexcrawl game that is about exploration will get a new dynamic if surplus food (and THAT is exactly what the different communities sell to the PC) becomes a little bit more expansive every time the characters buy it from the very same village. The next plan to explore the surrounding area might not only take the ruins of ancient cites into account, but possible locations of other settlements, too. The villagers of the characters “base camp” might have heard of those form other wanderers or traveling merchanta (or merchant caravans) that passed through their own community. If the GM wants an in-game element that keeps the characters moving from one place to the next, the increasing price for provisions might be it. After all, the settlement will not share everything with the characters as their own people will come first, as will the fact that winter will be coming and that the larders still need to be well stocked then.
2) It provides a natural “drain” for the looted riches of the characters
In lots and lots and LOTS of games (yes, I want to stress that, too) GM and players alike have started to wonder what their characters should do with all their riches. New weapons and armor? They have already been bought. Finer gear? That was acquired already, too. …donation to the church or the cult? Some roleplaying about feasts and drinking bouts? Some players do this, others have character concepts that does not stipulate such kind of behavior (sometimes because the player is a munchkin, sometimes because it would be out of character). Buy a house or a boat or a fortress or perhaps starting out one´s own mercenary outfit? Such things are good things, but sometimes go beyond the scope of the adventures the GM has up the sleeve… or the GM is comfortable with it in regard to his or her own skill in handling things. If food is established as not coming cheap the problem is at least mitigated.
3) It provides a motivation for the characters
“Get rich or die trying” is literal in such a situation. Raiding a ruin might provide enough loot to have a comfortable life for a month, but after that you can try to earn a meal a day as a farmhand, start waylaying honest folk … or you dust off your gear, get the guys and gals together again and look for the next find. If you are eager to proof your self and get rich (or die) quickly, you can go from ruin to ruin as quick as your wounds heal to become a legend… but if you fail, you might have to barter all the loot you gathered in exchange for food and bedding till the wounds have healed and you are ready to try anew. And THEN it is really “get rich or die trying”.