[foobarbecue]

Sunk cost fallacy. You aren't getting that $7.50 back. The question should actually be "do I want to, for no reason at all, feel like shit for the rest of the evening?"

(This assumes you aren't deriving any pleasure or utility from eating that last 25%. If you are, then that's one side of the cost/benefit analysis. But the initial cost of the food is irrelevant not matter what.)

[Aeolun]

I can ‘spend’ the money on the remaining 25% of food, or on not feeling shit (e.g. I didn’t ‘get’ anything for that money).

[foobarbecue]

Yeah. I suppose sunk cost fallacy here would be "I should eat it all to avoid wasting money." I guess you're sort of actually psychologizing OUT of that. It's still a bit fallacious, since the correct cost of the decision to not eat is actually $0, not $7.50, but I guess lying to yourself about that could be a useful mental trick.