Rations on ships during the age of exploration were typically of a type that would require little or no cooking. They included things like "hardtack" (unleavened bread), and salted meat, that could be stored for months without spoiling. Salted meat was "boiled" which required less fuel and lower temperatures than regular "cooking" (212 F vs. 400 F). The "fire brick" solution referred to in another answer was "suitable only for boiling," not for regular cooking. here