-Lots of walking, running, stretching, playing ball, ... at pit stops!
-Snacks! (non crumbly, such as grapes, fruit leather, gerber yogurt melts, cereal, and sippy cups that don't leak)--a small insulated lunch bag for fruit or sippy cups helps.
-Small magna doodle
-Toy phone that makes noise or music when you push the buttons
-Board books for him to look at (some old favorites that he knows and a couple newer ones)
-Kids songs on CD (I copied them from the ones I got a the library--I know I wasn't supposed to, but awesome to have when the day gets long in the car) -- save them for the 2nd half of the trip when you'll need them so the adults don't go crazy listening to them the whole day...pump up mommy & daddy music to keep the driver awake.
-Pacifier (if you use one) and lovey, blanket
-Window shade screens
Is he potty trained? You didn't mention, but it was a concern for us on our 10 hr drive this summer. We put a Pottete Potty Plus in the truck with us so we could just do the potty thing quickly. Or, put a waterproof pad/piddle pad in his seat, or just put him in a diaper.
I don't know the area, but I'd try to get the longest stretch of driving first. What we did is had the car packed and ready to roll, then pulled the kids (2 and 3 yrs old) right out of bed (around their normal wake-up time) still groggy and in PJ's and then let them eat breakfast in the truck on the road (zippy bags of rainbow O's cereal and a sippy cup, and freeze dried yogurt). We went 2.5 hrs in the morning before stopping for fuel.
You CAN do it w/o a DVD player. Have a safe trip!