[phil_]

Peanut butter sandwiches are cheaper than fast food, inoffensive, and relatively stable in a sandwich bag environment. However, nut allergies everywhere, so might not be suitable, depending on how micromanaging your bosses are.

Mickey D's sells one dollar salads, so that's cheap and leaves and not meat.

See if you can avoid sitting or standing still at your job to squeeze a little exercise into life, but, again, micromanaging bosses and your position as a replaceable cog might prevent this.

Have you considered a life in the jungle, living off plantains and manioc and wild game? You'll probably die before you're sixty, but that could happen anyway, and you won't be fat.