You don't want to go home for Thanksgiving or Christmas? Then you will know what you need and be able to bring it.
You can get a lot at USMA from the various stores.
Some of your clothing needs will depend on your sport.
Some years they allow plebes to travel in civilian clothing and some years they do not, so to some degree, you won't know all of your needs until you are at WP. But you will have shopping options near WP to handle those needs that you don't yet know about. Also, each room is allowed a few items like a coffeemaker, iron, etc.; the cadets usually divvy up who will bring what. So that's another example where you might not know what you will need until you are at WP.
West Point gives a lot of extra t-shirts and other clothing when celebrating certain occasions, in addition to uniforms. As 2026 plebe, my son just wore those and uniforms. He recently (March spring break) brought back home a lot of the nice clothes I mailed to him such as branded khakis and polo shirts. He says a lot of official trips they wear uniforms anyway. And weekends on pass, he likes to wear relaxed running pants and the Army tshirts. Depending on clubs you join, you may need special clothing but plebes are usually almost always in uniform when in public. Don't buy/bring much, there's not a lot of storage space as a plebe. There are several department stores within a 20-mile radius plus online shopping delivers in 2 days etc.