I’m familiar with the halacha that somebody working a vineyard is allowed to eat from the grapes of the vineyard and the owner can’t disallow him to eat.
Does this Halacha apply outside of the field?
How about by a pizza shop, is the worker entitled to eat pizza?
How about by a steak house?
The halacha that a worker may eat while he is working only applies, from when the food is ready to eat, until it is obligated in separating, maaser or challah. Therefore, in the pizza store, there worker may technically eat from the flour until it is mixed and challah must be taken. Once the dough is obligated in challah, or if it the dough will not be obligated in taking challah, (less than a shiur) then the worker may not eat from it.
Regarding the steakhouse, unfortunately it also will not be applicable as there halachos only apply to produce that grows in the field, and not to meat or milk products.
On the other hand you can ask your boss if he minds, if you eat a little. It is very possible that he won’t mind because he wants to keep up a good atmosphere in the store.
CH:M 337-2, 3.