I'd probably mix. Classics, Pixar (which borrow from a lot of more current music), TV and so on. If you are going to the darkside, throw in some songs from there like Hedwig's Theme, Despicable Me and so on.
* Go the Distance (Hercules) -- after all it IS a 4 hour drive and you're going the distance. Well, you get it.
* Hakuna Matata, Circle of Life, Be prepared (Lion King)
* Life is a Highway (Rascal Flatts, Cars)
* Star Wars Main Theme (Star Wars) (for a fun take, check out Science Wars online - -cute song)
* You've Got a Friend in Me (Toy Story)
* Spoonful of Sugar, Supercalifragalisticexpealidocious, and/or Chim-chim-cheeree (Mary Poppins)
* Part of Your World and/or Under the Sea (Little Mermaid)
* Be Our Guest and Belle (Beauty & the Beast)
* A Wish is a Dream (Cinderella)
* Heigh-Ho (Snow White)
* Real Gone (Sheryl Crow, Cars)
* If I didn't Have You (Monsters Inc.)
* Married Life (Up)
* Touch the Sky (Brave)
* Le Festin (Ratatouille)
* Define Dancing -- WALL-E
* Ballad of Davey Crockett (my kids thought this was just great, probably due in large part to the corny factor)
* The Nemo song (Finding Nemo -- timely given finding Dory is coming out!)
* Just Around the Riverbend (Pocahontas)
* He's a Tramp and/or Bella Notte (Lady & the Tramp)
* Got No Strings (Pinocchio)
* I wanna Be Like You and/or Bare Necessities (Jungle Book)
* Dare I put it out there? I do dare! Let it Go, although I prefer For the First Time in Forever and In Summer (Frozen)
* Once Upon a Dream (Sleeping Beauty)
* I'll Make a Man Out Of You and/or Reflections (Mulan)
* Down in New Orleans, Almost There, Gonna Take You There, Dig A Little Deeper, Friends on the Other Side (Princess & the Frog -- one of my favorite soundtracks)
* Bing Bong Song (Inside Out)
* Lava (from the Pixar short Lava -- think it's catchy)
* Incredibles Theme (the Incredibles)
* Whole New World and Friend Like Me (Aladdin)
* You Can Fly! (Peter Pan)
* Hawaiian Roller Coaster Ride (Lilo & Stitch)
* Zip-a-dee-doo-dah (Song of the South)
* What's This? (NMBC)
* When Will My Life Begin and/or I See the Light (Tangled)
* Happy Working Song and/or How Will They Know (Enchanted)
* Yo Ho Yo Ho, A Pirate's Life (ride song)
* Grim Grinning Ghosts (Haunted Mansion song)
* Jessie's song from TV show Jessie
I'm sure I've missed some major ones but that's what I have so far!