There are obvious items like clothes, medications, shoes, etc. that drivers will be taking on the road with them. But there is only so much space, and considerations have to be made for things like time of year, and type of job.
Every driver will eventually end up with his or her list of "must haves" for truck drivers, but we've got a lot of suggestions for you below.
Keep it small, keep it legal, and keep it necessary.
Wiki - Items To Bring To CDL School, Training, and OTR
As with most things, you "get what you pay for". It will be important, when feasible, to spend a little extra money for a better quality product. Functionality, dependability, and life-span are factors to consider.
Article - More on my First Two Weeks OTR - Including Things You Will Need With You
Make sure you bring 12 volt chargers and power supplies for your phone, ear bud, laptop, and any other rechargeable device you may have. My trainer's truck does not have an inverter so I use only 12 volt power supplies.
Forum - Making the Sleeper Cozy Like your Home
I'm not much of a decorator. I have a lot of books at home so I have one cabinet in the truck dedicated to being my mobile library. I switch them out with different books as I finish them and I get a little bit of that old book smell in the truck.
The main items that you will want to avoid having in your truck are illegal drugs, alcohol, and weapons, especially firearms of any kind. Drivers are legally prohibited from driving until 4 hours after consuming alcohol, and most trucking companies will specifically outlaw having any alcoholic beverages in the truck.
The web of different gun and weapons laws from state-to-state and jurisdiction-to-jurisdiction, along with most companies and customers specifically prohibiting firearms in their trucks or on their properties, make carrying guns or other deadly or dangerous weapons a terrible idea. Keep in mind that some states also ban stun guns, as well.
Getting caught in any of these cases could end your driving career, possibly forever.
Forum - Truck drivers with Weapons permits
Even if you are licensed, even if you choose to ignore company policy - you run a severe risk having a pistol in states where you are not reciprocal or worse - illegal.
Forum - Trucker Weapons/protection
What maybe legal in one city/state will be illegal in another. And then there are the company policies that says you can not carry a gun in a truck. Immediate termination from your job if you are caught and there is no appeal.
Forum - Truck Driver Drinking while OFF DUTY
Remember - ANY DETECTABLE ALCOHOL - is an out-of-service (OOS) - even if it's not a DUI. Most truckers won't even use an alcohol-based mouthwash.
Forum - Drinking in the Truck.
Most companies policy forbids having any alcohol in the truck. It doesn't matter if you're taking a reset, there's really no excuses. The only time you can drink is on approved home time.