Lets see... a handgun, a bottle of scotch, a years worth of playboy back issues
Seriously. Bring enough clothes to keep you going for a few weeks, but not more than can fit in a reasonably sized duffle. Bedding (or a sleeping bag) and a pillow, a comfortable pair of shoes for driving, a pair of boots for walking in the snow and muck, a pair of shower slippers. I good heavy jacket (and being you're pulling reefers, you'll want to keep that with you all year.) A good pair of leather or canvas work gloves (actually bring two, one for freight handling and such, the other for fueling and doing pre trips,) sunglasses, maybe a few books to keep you entertained, a charger for your cell phone, a hat (useful for those days when you don't get a shower,) a motor carriers road atlas (yes, your trainer will have one, but having your own allows you to do some studying,) a notebook and pens, a calculator.
Just remember, you are going out in your trainers truck, not your own. This means you don't need things like a CB radio, cooler or television. It also means you will have only a limited amount of space for your stuff (even if you're trainer is nice and tries to make room for you, there just isn't much space in the sleeper of a fleet rig.) You more or less are going to cram your life into a duffle and, with any luck, some of your entertainment and creature comforts will be provided by your trainer.
