I wouldn't overthink it!  A school is relatively short, so don't send too much stuff that he'll have to try and carry or ship to his first duty station. They study hard in A school, so having homemade cookies and brownies to share with the others is always a hit and makes you popular - believe me, they love it :)  Pack them in a plastic Rubbermaid-type box you can get at dollar stores that fit into the large-size priority mailing box, tuck in some Skittles and M&M's (also popular with our sailors), some encouraging notes from friends & family and you'll have a care package he'll be very happy to have.

Hi! My boyfriend is in A School right now too. I always send homemade cookies in ziploc bags stuffed inside rubbermaid containers and like Marcy said those are always a huge hit. He has no room to store anything, especially since all my letters from boot camp are filling up his drawers ;) so I keep the care packages simple with just food (jerky, candy, etc.) and cds. His favorite thing that I've sent him so far has actually been jiff peanut butter lol if you figure out a way to send pie I would love to know! I'm always afraid that if I send something like that it will fall apart. For fall, I'm going to try and make these banana nut bread jars :) http://10282011navywifey.blogspot.com/2012/07/mason-jar-baking.html