A way to pack for a road trip with an energetic ASD child is to create a separate tote bag with one change of clothes (for the entire family) for each day of your trip. That way you don't have to load and unload a big, heavy suitcase every day. I also like to pack a pool bag that I can grab quickly, and a small bag of toiletries (shampoo, deoderant, etc.). The pool bag should contain suits, towel, lotions, diaper, deflated/small pool toy, and flip-flops as needed.
Always have a backpack for your child with "busy time" toys, beverage, and at least one change of clothes within easy reach. Also, I like to keep at least two extra pairs of kids' shorts in the seat pocket. I do this for everyday excursions, not just road trips.
Try to keep putting your camera, maps, flashlights, books, and other gear back in the same place every time so you don't waste time looking for them during your trip. In other words, save time by trying to stay organized.
Save your sanity by investing in a portable DVD player. If you don't have one and you will be traveling, look for one during 4th of July, Labor Day, and day-after-Thanksgiving sales this year.
For my son, the best
For my son, the best investment we ever made was in a good set of noise cancelling headphones (which can plug into our portable DVD player and also into the TV/audio systems on most of the airlines). My son's face visibly relaxes the moment he puts these headphones on. I tried them myself on this last trip and I could not believe the difference in the quality of the sound coming through the plane's system! It also effectively muffled the ambient noise in the plane - I could just barely hear the child crying two rows behind us. I regretfully had to give them back to my son - but it warmed my heart to watch him sleep so soundly for the entire flight.
We also pack extra light and I schedule laundry nights. This is just a residual from my motorcycling days, but I find it so much less stressful to travel with a minimum amount of luggage I can possibly get away with. I layer clothes for the weather and only pack things that scrunch up well, can do multiple duty, and resist showing the dirt. We may not be the snazziest looking family on holiday, but we enjoy ourselves more without the extra stuff.