He's on a tight budget and an equally tight schedule. Store-brand or sale items can save him a bundle. For a few bucks, he can buy enough brown rice and pasta to feed a dorm. When he makes pasta or rice, tell him to make extra, which can be quickly reheated for lunch the next day.
Canned fruit packed in juice can also be easy on the wallet when fresh produce gets too pricey.
Tell him to buy produce that's in season for the best buys. Potatoes, carrots, and bananas are usually easy on the budget year-round. Ditto for canned vegetables. Have your son reach for the low-sodium variety to harness the salt. When it comes to dairy foods, buying milk in half-gallon containers is definitely cheaper than pints or quarts as long as he is going to drink it before it goes bad.