We are 15 hours away and our kids (9, 5 & 2) are road-trip warriors We've taken 9 trips to WDW since becoming parents and usually split up the drive about halfway and stay overnight at a Comfort Inn (usually we can get a promo like stay 2 times within a certain timeframe get 1 night free). I'm a teacher and like to keep things organized so I make an itinerary for activities. If I let the kids reach for whatever, whenever they want they seem to get bored really quickly. For the first hour we listen to a CD of songs we all like, sometimes DH will make a CD for us or it might be a kid's movie soundtrack that we all like and we talk about the trip since the kids are so excited. Then we break out toys like magnatiles, legos, etc. We have a snack and some electronics time. We will stop for a meal or eat in the car depending on whether I was able to prepare and make a meal. Afterwards our youngest will take a nap and our 2 oldest will read and maybe doze off for a bit. When our youngest wakes up they will watch a movie together. Then it is snack time again, the kids get to play with their toys and then have electronics time. If we drive when it is dark we break out some glow in the dark bracelets to keep them entertained.
I bought a BUBM electronics/chord organizer to keep all of the wires from our tablets/etc from getting tangled and always within reach. We bring our portable DVD player with a headphone splitter so they can all watch the same movie while the adults listen to our podcasts over the car speakers. We pack everyone's favorite snacks and make sure to keep the salt low and protein high (unsalted nuts, applesauce pouches, freeze dried fruit). This keeps everyone from feeling sluggish or bloated. We pack a separate small suitcase for the hotel we stay at along the way, that way don't have to lug in our large suitcase and dig through all of our clothes to find what we need.
Before we leave to drive home, each of the kids gets to pick a special snack from the resort store for the ride home (Mickey pretzels or a rice krispy treat).