I keep a sandvich around mostly so that if my medic gets hurt I can toss it to him.
Dis. Whenever I medic a heavy, it's very very useful to have them be able to toss me their sandvich.
Fo' sho'.
I alternate between Sandvich and Shotty when running with a Med. Both have their place. I try not to use the chocolate bar with a Med though, for the reasons I listed before.