My nephew was in Marine boot camp exactly a year ago and he said they deducted $300 per month from his pay for food.
$300? That’s a chunk but I’m not surprised.
Married military members may have gotten a Basic Allowance for Subsistence (BAS but commonly called "separate rations") after boot camp. That amounts to about $370 a month.
Your nephew would not have gotten that allowance while in boot camp because everyone has to eat together in the chow hall. He probably will not get it after boot camp if he is not married. But he gets the equivalent in meals eaten in the chow hall.