What to buy ahead of time , like GPS , Telephone Headset and anything else you can think of ?

A can of soup, and ramen noodles, and some napkins, and Walmart bags. You can do a lot of things with these items.
Don't forget a candle and blanket in the winter.

 

12v Heated blanket in winter , work gloves, roadpro tire thumper stick,

 

Only if you want at least one intelligent life form in the truck.

 

Forget the TP bring my some Dude Wipes

 

A CB, GPS, Atlas can probably wait till you get into a truck solo. You would be packing it around with you, or sleeping with it. You may not have any storage space on the truck, it might be whatever you can fit on your bunk (twin siz). I would keep it light so you don't have a problem carrying it around, two bags?

A wad of cash to float you through a bad time, like your debit card getting compromised. Unlikely, but possible. Up to you.

Shower shoes and towels, some of the TS shower towels are rank and mildewy. You can use them but you will smell like that after. If you team with someone they can get a "team" shower, two seperate showers for the price of one, just ask someone at the register/fuel desk.

A flashlight for inspections, maybe one that you can wear on your head.

Two cans of beans just in case you get stranded/detained and get hungry.

A big knife to stab people that park in the fuel island and then go in to take a shower.

No, seriously, I would keep it light for now. Sign up for reward cards from the truck stops. They give you points when you get fuel. You can use them to buy other stuff like electronics, laundry, food. Most of them you can pick up on the spot, TA/Petro mails them to you, and it looks like junk mail... If you team and get fuel you can still get points anytime you fuel, while you are training. Just use your rewards cards at the pump.

 

Take some freakin' tools with you. This guy that had a hubometer come loose on the wagon, and no tools, is just piss poor, I'm sorry.

 

I did that AFTER I got done with the trainer. The OP here has yet to get done with the trainer much less get their CDL.
Yes AFTER you have your own truck from whatever mega carrier you will want tools. Just remember to keep what you get light. Light as in not too much gear. You never know, the company may toss you at a moments notice. Or even you may not like the manure they are feeding you.

Otherwise good tools to have even after your done driving.
-Battery operated drill
-Set of quarter inch drive (for drill) bit set

-Quarter inch drive sockets (when the drill batter has died)
-a 3 pound hammer (really good for knocking stuck tandem pins)
-DONT BRING A MAG LITE! Get yourself a cheapy LED light that you see at counters of the hardware stores. That magnet mount with clip will attach and give you hands free lighting when you need it.
-Baby wipes are excellent in the morning when your windows are fogged up from your 10 and dont leave watermarks.
-A citrus type mechanics hand towels (in a can). You can use them in the armpits and then you wont stink when you go to the shipper/receiver. Otherwise your hands will get dirty.
-Tablet or notebook computer. A cheapy notebook computer that is, There are trolls out there that have nothing better to do than lock up a computer, so a cheapy you wont be afraid to wipe the computer and reset when it does / will happen. (never happened to me). This is great way at the truckstop or shipper for you to pretrip the load. Look at exits via google maps and see what the exit looks like. Look at your destination to know where your going at street view. Trust me, your brain will click better if you saw it before time.
-GLOVES!


Finally dont forget to breathe. The headaches of other drivers can be a interesting ride. Oh and dont forget to tell us of how your doing. It is a support group here.

 

Good suggestions so far but I'll add a couple of things. Once you get an assigned truck make up a little box of spare parts. Nothing elaborate but I'd include several glad hand rubbers, some brass fittings for splicing airlines, some basic electrical stuff including a cheap circuit tester, wire, and tape, a tail light or two, and some hose clamps.
You being an A&P, there's no point in my telling you how to use these things or what tools to bring.
You might go a couple of years and not need any spare parts but eventually you'll need every one of them or another driver will...and it's sure better to fix it yourself than to spend the night in Snake Navel Arizona for want of a fifty cent part.

 

2 years wrenching on small planes in Florida heat made me never ever want to see another Cessna again.

 

CB are "mostly" used to ask "what lane we need to be in" 300 times in 30 seconds AFTER everyone is stopped. I guess maybe 10% of trucks use a CB. 90% of those are used only after they are stopped in the road. Those radios are called "back-up radios." I can drive 2000 miles and hear the radio speak 3 orv4 times, besides the base stations 7 states away running big power.