Am current Plebe, I want to shed light on this to help out future teammates.
Bag doesn't really matter, whatever works best for you. Key thing here is to not over-pack. Bring 2 weeks worth of socks, (white PT socks) and at least 10 pairs of ACU socks, however many black they recommend should be fine. Make sure they are comfortable socks. You need to put everything in zip loc bags otherwise you will certainly not be able to transfer everything to your flight bag in time.
Other essentials: lots of underwear, 2 weeks worth is ideal, multi-tool is very helpful, make sure your boots fit nice and snug and are broken in (not too tight, but if your feet/boots are soaked, your foot shouldn't move a lot in your boots, otherwise very blister-prone), quality razor that will last, a good pair of running shoes (Nike Freeruns and most other nikes are not best), a watch that won't break (shouldn't be fancy, don't buy gps watches or smartwatches), lighter is nice, 10ft or so of 550 cord is nice (this can be obtained during beast though, mostly needed for field operations at Buckner), address book, envelopes, stamps, they give some paper, but bring a little more and another writing utensil, roll of army green duct tape, bring a little soap that you can wash clothes with, you will want to do this when you can't do laundry service
Those are all the things that I can think of off the top of my head, now for some things you don't need:
Court shoes (these MUST be acquired immediately following beast during re-orgy week, however), don't need a lot of extra nametapes (they issues two of each, it is nice to have extra, however), don't bring a picture frame, just some pictures,
The thing about CBT is that it is a very short portion of your West Point experience and although challenging, it will prepare you for what comes, just focus on getting through beast and all the things that you may need during the academic year, you can get after A-day, for now, focus on getting through beast and worry about everything else later.
Best of luck