A birthday on the road is a phone call and a thing that arrives when it can. Plan for the date he will actually open it, not the date on the cake.
Match the gift to where he will be
If the route is known, a meal voucher he can use at a chain along that route is easier than a cake. If the route is not known, send the gift home. A parcel that chases the truck usually loses.
The same rules as the other gift notes apply. No surprise wiring. No second flashlight if the first one is already in the door. Ask what wore out. Gloves, a towel that can dry, and a decent headlamp for the walk-around are boring and therefore good.
On a phone, this table moves sideways. The first column stays put.
Birthday timing, not a shopping personality quiz.
He will be
Better gift
Worse gift
On the road, route unclear
Something that waits at home, or a card he can spend anywhere
A perishable box with a delivery date
Home that week
The meal, or one cab item he named
Another mug
In a team truck
Two small things, or one that does not take the only socket
A bright lamp aimed at the other bunk
Conclusion
Call on the day even if the box is late. The present is the fact that you knew where he was.
FAQ
Should the gift be a joke about trucking?
Only if he likes that joke. A useful object beats a novelty he has to haul.
What if I do not know his truck?
Buy something that does not mount to it. Pocket items are safer than brackets.