He should carry enough cash for an emergency as well as the incidentals. $300 should do it. A debit card means he has to find an ATM, which can be difficult, carries the same risk of loss as cash, and is too easy to lose. For extra security, have him split the cash into two locations, preferably zippered on him.
Going forward, have him open a checking account with you as co-signer, since he's still a minor. Your bank or credit union should have accounts that do not charge monthly fees or waive them if you are doing a nominal monthly direct deposit. The account should also have a debit card that draws against it -- do not do a prepaid card other than what's in the account. I would opt for an account with a minimal number of actual checks -- too many young people have no idea what to do with these. Finally, help him open a credit card with the bank or credit union, again with you as co-signer; this should offer a nominal cash back reward & be set to a minimum credit limit, like $500. Have him use this CC to pay for his gas & other purchases, and only use the debit card to get cash. He must pay off any charges every month; this builds good habits as well as a credit history & you don't care how much the APR is because he should never pay it. BTW, you can transfer any allowance to his checking account but do not pay off any credit card balance for him -- he must take responsibility for doing this himself. By being a co-signer, you can keep an eye on how he's doing online while he's still under your roof.
