"When you go [to work] in the vineyard of your friend, you may eat
grapes as you desire, to your fill." (Devarim 23:25)
The Torah gives us guidelines as to when and how to allow workers to snack
from the produce thay are processing. The workers, however, are cautioned
not to overeat, thus taking unfair advantage of their employer. They may
refrain from eating until they get to that which they desire more (Rambam,
Hilchos Sechirus 12:11)
The worker may not take food for his wife and children, only for himself
A worker may not work both during the day and at night, for then he will
not be fully functioning for his employers. He may not starve himself,
for then he will not be able to work energetically (ibid. 13:6).
A worker must be careful not to waste any of his employer's time.
Similarly, he must work with all of his energy, as Yaakov Avinu
said: "With all of my strength, I served" (Bereishis 31:6). This is why
Yaakov became so fabulously wealthy (Rambam, Hilchos Sechirus 13:7).