Three issues here…
Body temperature should keep food from freezing unless its extremely cold.
The fire doesn’t seem to affect the ambient temp inside the house.
Food shouldn’t freeze above 32 degrees.
Seems like my liquids are just cold and the food is all frozen… That is pretty backwards.
food is based on ambient temperature for the square you are on
want your food thawed use something with cooking quality like a pot or a pan to heat it over the fire
Well the system is way too broken all the same as Ko explains. Hope a plan is in the making to make this caveat about inventory freezing less…freezy. 
If your characrers body would be so badly insulated that It would keep an backpack full of stuff from freezing then the character would likely freeze to death if the temperature is harsh enough. Either you keep your surroundings warm with your body heat or your body