The food rations Rey ate to survive were the direct result of Unkar Plutt raiding what was left of Imperial and New Republic battleships. So, in essence, Rey was literally living off events that happened in the past. As a scavenger, this makes sense. But the equipment she was trading to eat was just allowing her to purchase food, which was itself, scavenged in the first place.
A new tweet from the offical Star Wars Twitter account points out that Unkar Plutt’s ration packs — the currency of the Niima trading post on the planet Jakku — were originally salvaged from both New Republic and Imperial military kits. Meaning, if there hadn’t once been a huge battle between the remains of the Empire and the New Republic above and on Jakku, then seemingly, there wouldn’t have been a huge surplus of food, either. Unlike the desert world of Tatooine, it seems there’s very little indigenous to Jakku.
So, just like that X-Wing fighter helmet and the AT-AT she lives in, everything in Rey’s life is a leftover from the generation before. Hopefully the adventures she has in The Last Jedi won’t be as secondhand as her food.