It really depends on you. I know guys that spent maybe $1 a day. Granted they were in scrounge mode the entire time and probably forgot they graduated from college and could afford real food...I knew a dude that hit up SAM's club the first weekend there and probably spent $40 dollars the entire month.
Other dudes would be going out to eat 2x a day and would easily blow by their per dium.
I would probably eat at the golf course every other day, the chow hall 90% of the dinners during the week, and go off base for the weekend. So figure you are spending no more than $50 during the week on food and then whatever you want for the weekend. My average bill at the chow hall was less than $5 a meal.
This doesn't include booze.