I'm wondering what I should pack away for a later time and what to donate/sell.

Beside things with sentimental value.

I mean items like gaming console, stereo, home computer etc.

I dont want to sell things like this only to find I would be able to use them later then rebuy them.

maybe its dumb to think I will have the privilege of playing Xbox once in awhile in the next few years

Keep as much as you'd like.
At your 'A' school the barracks are going to be relatively similar to college dorms.
If it looks like it would fit into a college dorm room you will probably be able to fit it in your barracks room.

My students all seem to have items such as the following: Computer (desktop or laptop), XBOX, Playstations, Smaller TV's, collection of DVD's (like 40), couple of books (20 is the most I've seen in a barracks room), electric guitars, acoustic guitars, box of tools for working on cars, Dresser full of civilian clothes, and so on.

I would recommend tossing or donating anything that requires regular replacement anyways. You civilian clothes may not even meet requirements for wearing on a military installation, and thats something you should be buying new occasionally anyways.
The expensive electronics I would keep, but remember, you will have to store it somewhere since you won't be allowed to have it until you are at 'A' school.
And remember. . .the barracks are not so large that you can get crazy. I recommend DUAL-purpose electronics. (Make sure your computer can play DVD's/function as a stereo. . .that type of thing)

Most 'A' schools won't allow civilian clothes/fancy electronics privileges until you pass a probationary point. (Commonly referred to as Phase I liberty status) Typically Phase I liberty is between 2 and 4 weeks last time I talked to the instructors who deal with those students. It may vary a little from schoolhouse to schoolhouse.

The other concern is that surface sailors still live on ships at the junior paygrades. . .you will have to talk to a surface sailor to understand how much space they have on board. (You are entitled to BAH at the Paygrade of E-5 or as an E-4 if you have more than 4 years of service)

ALL submariners get barracks. . .so even if you are underway on the ship your stuff has a place to live. BAH just means you can live out in town.

Thank you so much!!!!