Its his job to deliver items to you and gets paid by the company to do so.
Now that is not to say if he goes above/beyond the call of duty, delivering to you first if you have a rush need, helping you move items once off the truck, etc...
Instead of "tipping" with monetary value (money) why not use your skills as a designer/sing-maker to do something unique for him.
Say he is a hockey fan, make him a custom decal to place on his window or if you do heat press shirts a custom jersey