Phrases for filling stomach
Satisfy my hunger.
The word satisfy is commonly used here, including this definition from TheFreeDictionary:
to put an end to (a desire, want, need, etc.) by sufficient or ample provision: to satisfy one's hunger.
fulfill my caloric content
More technically accurate and not completely unrealistic to hear said in a sentence.
Sustenance: something (such as food) that keeps someone or something alive.
"The food was so bad that I couldn't eat even for sustenance."
One could also use survive/survival.
"The food was so bad that I couldn't eat even just to survive."