Easiest ways to get food that i've discovered:
Centaur encounter: Beat her in a fight and then give her a blowie, easy 100 food.
Sleeping Ettin: Wake neither, stay silent, wait, eat it anyway, easy 180 food.
Goblin Horde: Get discovered or go to the forest, offer them sucky sucky yum yum, easy 80 food.
Dryad: Self explanatory, 20 food if charisma = 8 (or if you polish her knob, it's also -5 health), 30 if 9.
Harpy Swarmer: Easy 20 food, easy fight.
Then there are the "Milk?" carriages in the 3rd and 4th map, they'll also net you a good amount of food.
Most of these are not suited for the pure runs however, although that sleeping ettin one doesn't require losing virginities, but they're completely free, well in monetary sense atleast.