Baba Metzia 7:4-5

Baba Metzia 7:4

If a person works with figs, he is not entitled to eat grapes; if he works with grapes, he is not entitled to eat figs. A worker has the right to refrain from eating until he reaches the place where the best produce is and then to eat there. A worker may only eat during the time of his actual work but if he intends to “return a lost item to its owner” (i.e., he's being careful with the employer’s time), then he may eat while walking from row to row and on the way back from the winepress. Similarly, a donkey is entitled to eat while it is being unloaded.

Baba Metzia 7:5

A worker is entitled to eat even a dinar’s worth of cucumbers or dates (i.e., as much as he likes, even of expensive produce). Rabbi Elazar Chisma says that what a worker eats may not exceed his salary; the Sages say that doing so is technically permitted but they discourage a person from acting gluttonously because this will keep potential employers from hiring him.