DS had plebe summer last year. I sent a lot of protein bars ( usually Clif bars). We avoided a brand that advertised they had hemp seeds in the bars. Read the labels carefully. He didn't like the powdered sports drink flavors " too messy and take too much time to add to the water, Mom"; instead he wanted and I sent the small bottles of water liquid flavorings instead., available in the "sports drink " section of "nationally known discount supercenter store" or online from the same store. I also sent an extra bottle of body wash every two weeks- I figured he could use it with the humidity, the sweating, and all the physical workouts and if he couldn't use it someone else probably would want it. I also sent a pack of gel inserts for his shoes- he complained about those at first but later admitted he had been glad to have them. Be sure to break in 2 pairs of running shoes before you leave. Take one pair to I-day; your parents can mail the second pair to you after 3 weeks or bring the second pair at PPW- the pair you take to I-day will be trashed by then.
Cards, comics, short letters are always welcome. I copied inspirational and humorous quotes from a "famous quotes" book at the library onto colorful index cards, and mailed one or two a week. I did send stuff in a plastic box because that is what a social media parent site recommended; we found out later plebes were issued a plastic box. Oh, I sent a couple of mousetraps because Bancroft does have mice, but my opinion is the mice are mainly outdoors until September -October and then they move in to spend the winter. One of the moms of a female plebe recommended that females bring a hairbrush with them- faster than trying to tug a comb through hair.
Compression shorts were asked for a lot, have your plebe pick them out before he leaves and then you can send them . We mailed the first package the day before he left so that he would receive it about a week later. We live in the southwest U.S., it takes 6-8 days for a package to reach USNA using USPS if it is not priority mail.