if there's no health problem for your son, don't worry too much about learning ABCs, i think he listens to the school teacher more than you, just like my daughter, she's now 3 & a half years old, she remember all the ABCs after started K1. you know i started teaching her when she's 2 (which is a bit late already), but she can only remember few, so maybe you can talk to his teachers and tell them about your worry, maybe they can pay more attention on your son.
about eating outside, i think when he's getting bigger, he'll change his habbit, just try slowly and little by little, let's try to order his favourite food.