Continuing the suggestions, although a little bit afield from original question:
COPIES COPIES COPIES....
Copies of their paperwork...
Copies of drivers license and credit/debit cards and other banking cards...
Copies of passport info, of anything you can think of.
A nice folder/folio for DS to take with him.... with identical copy w/parents.
SOME (foresighted, not US) parents take a good pic of the kid, and get an enlargement... and have it around for those family times when the kid isn't there, but is 'present'(sorta) at birthday parties, cookouts(they will miss those a LOT), and other events. Best one I saw was parents who had their kid's pic on side of the grille with big juicy steaks cooking [ this may have been torture for the kid during indoc
... still, I thought it was brilliant ]
Get lots of pics of them smiling/laughing/doing fun things... you both will need to be reminded about that (during Indoc, during some of 'those' phonecalls home, etc)... They will be smiling and laughing plenty up there, it's just that PARENTS won't see 'em then, and that won't be the face you imagine during some of the phonecalls.
It is an experience like NO OTHER... And I admire every kid who has the gumption to test their mettle. Not all will make it, but every ONE of them will learn important things about themselves.