Unfortunately you wouldn't know what foods he needs to stay healthy and to survive - already he is probably very hungry and it's very important that he not eat the wrong things at such tender young age. Do you know if there is a wildlife rehab center near you? You could call one I know of in NJ for advice - they help baby squirrels all the time. (I know you're too far away to actually bring him there but maybe they can advise you over the phone or help you locate a rehab center near you). The center I have in mind is Mercer County Wildlife Center in NJ at 609-683-6606. Tell them a very young squirrel came right up to you - very friendly - tell them about how many inches tall he is - tell them you put him in a box (and when you did that so they know how long since he's had his mom and food) and ask what the best way is to help him now.
JJ
JJ