They seriously don't need anything expensive - not for a while.
Depending on what academy they will attend - there may be things they may want to buy to bring for the summer or academic year but these are not really "gifts".
For USMA there is opportunity to get gift certificates to be used at the cadet store. Anything that would qualify as a "gift" they probably won't be able to have for a long while.
I forgot about watches. I am pretty sure cadets at West Point can wear watches during Beast. Just get a tough waterproof one - it does not have to be fancy. It helps greatly in identifying your own in all those pictures....
My daughter got a pink (yes, pink) Timex sport watch a year ago for about $30.
It went through MMI and Beast and keeps on ticking...
I would not suggest spending a lot of money on a watch for Basic. A plebe might like a nice one for the academic year, however.