As a 42A what Military schools do you suggest I can do as active duty?

Any school they'll send you to. Air Assault is a great one. My biggest regret is getting injured before I could go. Pathfinder is also great and to get it you need Airborne or Air Assault. SLRT, Sling Load Certification is a great school. No badge but great skills. Since you are going to JRtC I am assuming you are in a light unit. You'll be an asset.

Casualty Affairs course usually available from Troop Schools on post. You'll likely need t go to some sort of USR training course as that will likely become part of your monthly routine. F5 ASI for postal operations, especially if you go to an HR Company as opposed to a BN or BDE S1.

Unless you are looking at Airborne or Air Assault which are probably best straight out of AIT (if your are thinking about one of those two, contact the AG SGM for the either 82nd or 101st, being HR they may have some advantage in getting an AIT student re-routed their way that other branches may not have) you are probably putting the cart before the horse. If you are projected for a F5 (mail) position then they will keep you at the Soldier Support Institute after you complete AIT to complete that course. Otherwise, it is unlikely you will see a resident course during your first year at your permanent duty station unless it is local training to fulfill and additional duty appointment.

Specifically as a 42A, postal operations, ASI F5. It will open up some additional duty locations for you when it's time to reenlist