I'm a bit late to this, but a couple of things we did when the kiddos were younger:

1. Favorite blanket, pillow, and stuffy
2. A sunshade for their seat
3. Ask at EVERY rest stop, "Who needs to pee?" and then stop at every single one if needed...(and then everyone gets out to stretch even if they don't need to pee)
4. Love the ideas mentioned above about small toys wrapped up. We did variations on this.
5. They each get to pack their own shoebox (e.g., 6 qt Sterilite Storage Container ) with anything they want.
6. Play the license plate game.
7. Headphones for any electronics that are coming AND the car charger or inverter for said electronic
8. Hotspot or one of our phones in hotspot mode

The longest trip I've gone on with my son has only been about 5 hours and it was after he was past the potty-training stage, so I can't really comment on something like a 30+ hour trip with toddlers. That said, I found it really helpful to play podcasts and music that are interesting to kids during the drive. We loaded up my phone with stuff like "Wow in the World", "The Adventures of Finn Caspian", "Caspar Babypants" (Chris Ballew from PotUSA), and They Might Be Giants. Basically stuff that isn't super irritating for the adults, but will keep the kids entertained. We did have to take regular rest-stop breaks, but it worked pretty well and wasn't nearly as disruptive as I anticipated. Also keep in mind that with younger kids especially, they will probably end up sleeping for long stretches of the trip anyway. Sitting in a car for long stretches is more tiring than it seems. Plan to take regular breaks just to stretch everyone's legs, even if they don't have to go potty.