Food, drinks and other edible objects can be found scattered across the various sectors of Arulco, with cities having the most abundant supply. Most of these items can be found lying around in houses, shops, shacks and other buildings (even in trash cans!) and are free for taking, but some merchants may carry a limited supply of foodstuff and will sell them to you at generally low prices.
Consumables affect your mercenaries' current maximum stamina. As of v1.13, mercenaries lose stamina while traveling in the World Map or running about in hostile sectors, making edible objects an important aspect of gameplay. Eating the right food and drinks will let mercenaries instantly recover some lost stamina, up to their individual maximum stamina, while eating the wrong food, drinks or even objects (like spiders, for instance) will instantly lower their current maximum stamina (but never less than 0). Mercenaries with low to zero stamina cannot run.
Some objects are heavier than others, but the stamina recovered/lost is not in any way proportionate to their weight. The healthier food and drink choices in real life, like "fit" cereals, fresh meat, juices, fruit and vegetables, tend to recover more stamina than "junk food", like snacks and beer. If you anticipate traveling long distances where food and drinks are few and far between, bringing lighter yet "stamina-rich" objects not only helps recover lots of stamina but also frees up some baggage room for your mercenaries to carry other important things.
↑ 5.05.15.25.3These values do not seem to match the intended purpose of the corresponding item (i.e.: an expired consumable giving a positive boost to Stamina). This is probably due to an oversight from the developers.