Specialized shops only buy the kind of item they sell, so Munxip will only buy food. You can get gold by killing monsters, as in most RPGs, and most of their corpses are surprisingly tasty (just stay off kobolds and rabig dogs). Large and iron rations are a pretty common item too. The Infinite Dungeon, a tiny distorted cave in the southeast part of the map, is a low-danger zone where you can get items, money and experience levels. Just don't dive too deep. Or you can take the puppy and/or carpenter quests and explore their first levels, which might be a better idea since they're closer to Terinyo and time passes much more quickly when you travel through the wilderness (i.e. hence you get hungrier soon).