OK, you asked for more tips, so here goes....
~ This is a tried & true for me on countless trips solo with the kids: get an extra early start! Load the car the afternoon before in the daylight, go to bed early (if you can wind down
) with everyone in the clothes (sweats/tees) that they are going to wear for the first leg of the trip. Get up around 3:00 or 4:00 and just leave. If you are lucky, DD will either fall back to sleep, or at least be pretty mellow for the first few hours. The sunrise will help YOU feel refreshed a couple hours after you hit the road, and soon after that you can stop for a nice breakfast/stretch break. I love getting a good 3-4 hours of driving out of the way without feeling like the day has really started. This can serve one of two purposes... either you can get a lot farther than you planned because of the early start OR if you need to stop sooner than you hoped, you should still be ahead of schedule.
~ Pre-made snack containers. Tell DD that each container has to last x amount of time. It's funny but if my kids know there is an endless supply of snacks, they keep asking... but if they know they have to be responsible for their own and want to have it when they're truly hungry, they make it last.
~ Extra pillows to lean on, and a Snuggie rather than a blanket if you will be driving when it's cooler (i.e. making an early start). The Snuggie is less likely to fall on the floor, and is nice to cuddle up in.
~ Neck cushions for the seatbelt (yes those tacky looking things you can buy with velcro strips at any gas station). I remember the first time I took DS back to my parents and arrived 12 hours later with what looked like rope burn on my neck. My parents took pity on my and gave me the chamois seat belt cushion from their car so I could have it for the ride home.
~ If you are going to stop for an overnight, pack a SEPARATE bag so you don't have to unload the car to get to the giant suitcase you are taking to WDW. A large backpack, small duffle bag, or rolling carry-on size works perfect. I always put this in the front of the car so I don't have to open the hatch and announce to the world that I have a van filled with interesting stuff.
~ Elastic waist pants for everyone. They are much more comfortable to sit in on long trips.
~ Set ground rules for breaks before you stop. We have a "no, we aren't buying any stuff at rest stops" standing rule, but I also make sure they know for each break what to expect... "This is a potty/stretch break, we'll be back on the road in 15 minutes." or "This is a meal break, we can relax a bit." or "This is a super-quick 'mommy needs to potty' break."
~ Pack a separate tote for the front of the car (I like to have this on the floor of the front passenger side so it's easy to get to, but the kids aren't stepping on it). This is for with things you will want handy but tend to get in the way [or lost]... wet wipes, paper towels, water bottles, snacks, cords for any electronics, a camera (keep that handy for the fun shots along the way!), etc. Then when you get to your destination, separate what you need for the week from what you won't need again until the drive back, including those extra pillows, snuggies, etc. Pop the cover on and throw it in the trunk/hatch. It's out of the way and ready to go when it's time to hit the road again.
~ If you don't have
AAA, or something similar through your insurance, it might be worth the investment. A flat tire tire with kids is NOT fun.
~ Keep $20 someplace in the car (and a CC if you have an extra) that isn't with your purse, just in case your purse is stolen/lost. Also write down the phone numbers to your bank and CC companies so that you can call them right away if needed.
~ Downsize your purse &/or get a small bag for the trip (a Baggallini is great!). Leave your gym membership card, your local store discount cards, etc. at home. Take only what you will need.
~ Put one of those magnetic emergency key holders under the car. I won't leave one there for regular day-to-day use because they're pretty easy to find if someone is looking, but when on a road trip I'm willing to take a chance rather than need to call for someone if my keys get lost.
~ If you have multiple kids, dress them in matching shirts. I like to use cheap tees (that I don't care about staining) in a bright color. We often get comments from strangers like "ahhh, look at the matching shirts" but the truth is it's easier to keep track of them in a crowd, and I've always been aware that if one was separated it would be easy to say: "he's wearing 'this' while pointing at a sibling". Along the same lines, the boys know that if we are using a public restroom, they STAY TOGETHER. If one is taking longer, the others wait by the sinks until he's done. And DD knows that she and I walk in together, and walk out together.
~ Probably goes without saying, but make sure kids either know your number AND one other adult's number by heart, or if they are too young, order a dog tag with your pictures on 1 side and the numbers on the other (we used artscow.com, they're cheap and hold up really well!). Remind kids who it's OK to talk to at different places (CMs at WDW, Moms with kids pretty much anywhere, police officers, etc.).
~ Take a Kool Aid container from the dollar store that has a cover. It is the BEST vomit catcher because it can hold a lot, it's deep (no spillage), has a handle for the sick person or for someone helping a younger child, and the cover will keep smells to a minimum until you can wash it out.
I might think of more, but that's probably a good start
DH never has time off in the summer so our 2 DDs and I have driven down 3 summers in a row by ourselves. This year will be our 4th. The only thing I make sure I do is find a place to stay before it gets dark. I'd rather not be driving around in the dark trying to find a hotel. We drive from CT and stop once overnight each way. 
We stop in lots of places in GA and prefer to sleep there vs TN. Never had a problem except the rest area after dark.
I am subbing to this thread as I would love any and all info about traveling to the world solo with the kiddos. Now, my next ? May be OT but anyone else care to provide any tips for touring and managing the kids alone? TIA
