Oh that's not too bad of a ride.
Dunno if you'd call it fortunately or unfortunately, but since I was 10 I've been trained to think that 8 hours is a short car ride. I wouldn't even bring anything on a 4 hour car ride lol. Anything over 4 hours I bring a backpack with snacks, water, book(s), paper, cell phone (with headset) and charger, cds. For my college years I had my cat, so I'd talk to him a lot.
I live in the U.S., and I'm not sure where you're at, but my dad and I used to keep track of what state license plates we used to see. We'd write down all 50 states, and cross one off each time we saw a plate from that state.
Or, you could play the plate alphabet game - You have to find the alphabet on license plates. Each person keeps track of their own alphabet, you have to say it out loud, and no one can use the same letter on the same plate. (example, everyone starts at "a", and if a car drives by that has an "a" on it, only one person in the car can use that "a". They go on to "b", everyone else is still on "a".) We played that so frequently that we started "banking" hard to find letters.
So if after like half an hour someone was still stuck on "Q" they'd try to take one from their bank lol! But we never allowed that, we were just joking.
Another one we used to play, but not that often, it's better on longer trips like 24 hours or more, was to each pick a thing or place, and count how many we saw, and whoever saw the most at the end of the trip won. I suppose you could pick easier things like a certain fast food place, or a certain car dealership, or how many construction sites, etc. It wasn't little things like "how many blue trucks" though.
I think all our other games or things to do require something you would need to buy or get a hold of. Like there's travel bingo. It's been a long time since we played games though. I know they sell travel versions of most board games that are magnetic if that would work for you. There's always books on cd or tape, but I never personally got into those... I read too fast and the books on cd always never seem to go fast enough for me.