Start with just the packing list. Go on your fact finding mission - search this side and for parents the Facebook groups for threads on what else you might want for I-Day, A-Day, and later for the school year. I think there was a meme for a 14-in-1 bottle for the males. Hilarious! For extras, DD packed feet blister things, stamps/a few envelopes/paper/address list/passwords list, and a comfort grip for the backpack handle.
Candidates, clean your room and label stuff. This will make it easy for parents to find your shoes, Calc/Chem notes, favorite wubby(ies), school supplies. For parents not visiting on A-Day: One Medium Size Box. Don't be That Parent that sends 4 boxes o' stuff and clogs the mailroom. Your DD/DS should be buying stuff him/herself and learning to be resourceful - How to Get Stuff - Cadet store, older Cadets/teammates with cars, amazon, where and when to go for delivery services (Arnold Hall). Parents learn the options of Getting Stuff to my Cadet: delivery services (AOG and Cadet Delivery Service, for example), sponsor family, sometimes through the mail, make friends with local parents (ex. who's going up and can take a box!). And anytime you pack for your Cadet, save some precious space for community gifts - ie, so your Cadet can share with others, esp. those in his/her squadron with no family support, etc.
For parents, remember everything is squadron specific. Don't freak out when you see posts that My DD this, my DS that....tune out the noise and learn to respond to What Your Cadet Thinks is Important. Don't ask What about, I heard, Have you done/seen/heard...there will always be Those Parents Facebook Bragging. For example parents pontificating Look How Awesome My Cadet Is! And then later they bust themselves saying it's the first time their kid passed the PFT, got on an Honor roll, etc. If there is one thing I think is most important, it is to train your DD/DS to always think glass half full. Coping and delayed gratification work their way to the top of necessary skills to get through BCT. USAFA and life, for that matter.