What you are describing is entirely normal, and happens in every division. There's always someone who can't figure it out quickly, but they eventually do. Stay supportive and tell him to hang in there. His division should start to click soon. It is all part of the process!
The first three weeks are the toughest. Believe me, no matter how well they're doing, they would be getting in trouble for messing it up. All part of the process.
When/if he calls, just support him and tell him to hang in there.
On the other part, why would he be needing cash?
My 2¢: Start send him money now and you will be sending money for his entire enlistment.
Daughter bought a car, bought a condo, flew home on holidays, earned a college degree without asking us for any financial assistance. The Navy is a well paying job with great benefits. And they teach recruits about financial responsibility in boot camp.
I agree. They are issued an NEX card to use when they are taken to the exchange; it comes out of their pay. They are not really supposed to have cash on hand in boot camp. No reason for it except to buy junk food he does not need, or to gamble.