Details: The quality, cost, and availability of food varies dramatically on many factors; but in any establishment (however informal) that exchanges gold coins for food, 3 gold coins can typically buy food of sufficient quality and quantity to satiate a humanoid creature for a day.
This average cost of 3 gold coins per Food also factors in the portability and freshness of the food in question. 1 Food can be assumed to be edible for at least 30 days after acquiring (varying based on the food, at Zaldar's discretion), and can be safely transported in hand, pocket, backpack, or otherwise without spoiling or being damaged.