i feel your pain, cause i used to work in restaurants/bars, and its a pain in the ass to eat right. yeah, you're legally supposed to get breaks, but in reality they schedule restaurant workers when its busy, and let them go home when its not. they do that instead of have you go on breaks.
anyways, i had the same problem, and when they told me i couldn't drink a shake behind the bar, i told them that in exchange for me not reporting them to the labor board for no breaks, they would let me drink my shakes. never had that problem again.
if they say you can't have food/drink on the line because of the health code, then just put/hide your shake or other meal in one of the fridges and sneak off every once in a while to eat.
good luck, and good luck getting out of the food industry. it's hard to leave since it's easy money, but just think, in ten years you'll be making the same amount of money you're making right now.