I think Pimp gives some good advice about bagging your food. Sometimes that's what has to be done. And like Pity said they have to give you atleast a 15 min break ( prob twice in 8 hrs ) to eat or smoke or whatever.
But lets say they don't. Protein Bars
, beef jerky ( which your doing) Nuts ( 1 cup of nuts is 1000 cals give or take a few ) , or some fruit.
The best thing would be to cook your food in advance and bag it.
Goodluck - it can be discouraging at times , but there is always a way.