In the past 2 years, we've taken 2 different summer road trips. In 2007, we spent two weeks driving around Tennessee, Pennsylvania, and then driving down the East Coast back to Florida. The kids were 2 & 4. Last summer (2008), we took a 3-week road trip out to the Grand Canyon. (You can read about it in reverse here, if you're interested.), and the kids were now 3 and 5.
Our survival was due to really good planning. I can subdivide the planning into three main categories:
For each trip, we only had one crazy 12-hours-in-one-day-drive, as that's how long it takes to reach the family in Tennessee. This only worked because we were staying at my in-laws house, and we did not have to drive anywhere else for a couple of days, so we had time to recover.
If you plan on driving every day or every other day, plan to be on the road only about 6 hours a day - possibly 8 if you're having a particularly good day, but that's really pushing it. Remember, you are on vacation so that everyone can relax and enjoy themselves.
As far as WHEN in the day to travel, I found that we could get rather far if we immediately left when everyone woke up - it would take a while for the kids to eat breakfast in the car. That's a little exhausing, however, and not good if you are on a long vacation.
Next option - leave after breakfast, and get a few hours in before lunch. I found that it was much easier for the kids to entertain themselves (and/or each other) early in the day so they were fresh, but after they had some food and a little running around under their belts. And if we got on the road a little later than that, they would last a couple hours after lunch without whining as well.
We were usually not on the road for more than 2-2.5 hours at a time. After that, someone had to use the bathroom, or we were just wiggly.
Activities (in the car)
When I packed the car, I put a big box of books (that they helped pick out), magna doodles, coloring books (new from the dollar storel) and crayons in between the kids. I also packed 2 small bags of little plastic figurine toys & cars - they did all sorts of role playing in the back seat with those!
I kept some other things separate. Up front with me I had a bag containing things like markers, blank paper & rolls of stickers (the stickers got everywhere, but the kids had so much fun with them that I didn't mind). I had 2 magnetic books that came out when when we'd been on the road for 2 weeks already.
If I'm not reading, I like to do things like sudoukus or word searches. This past trip, both kids liked to do word searches as well - the dollar store always has puzzle books. For them, it involved mostly just looking for certain letters on the page, but they pretended they were just like Mommy.
We do have a DVD player, and we splurged a little bit on one that has 2 monitors, and can even play two movies simultaneously (though we haven't needed that feature yet!). However, in an attempt to a) encourage our children to use their imaginations & entertain themselves, and b) preserve our sanity in the midst of late-afternoon crankiness, it was not allowed to come out until well after lunch. Many times, it was incredibly helpful as we tried to do that last push in order to reach that day's destination before dinner.
Activities (on the road)
In the US, the first rest stop when you cross a state line usually features a welcome center. We stopped at lots of those - the bathrooms were generally nicer, and since it's a welcome center, it's a tourist spot. They have all sorts of maps & brochures to help people plan your visit - we'd always let the kids pick out a couple and then they could read them in the car, draw on them, and it was nice for them to have something new to look at. Sometimes they even had coloring pages especially for kids!
Make sure you have plenty of snacks - and a good variety of stuff as well. It doesn't always need to be crackers - things like raisins & dried fruits travel very well & are a bit healthier. I found some tasty granola bars that had yogurt on top - dairy & grains! Carrots, little grape/cherry tomatos & celery (if yours will eat it - mine won't!) will travel for a while without refrigeration. I also brought those individual servings of fruit (don't forget the plastic spoons!).
Pack your food into a cooler, but make sure you figure out if you will regular access to ice, as that will affect the food you can bring. Remember - most places do have grocery stores if need be.
Keep in mind that if you are doing very large distances in a single day, your children will NOT be interested in sitting down at a rest stop & eating lunch. And really, who could blame them? Personally, I was always willing to let them run around the rest area & burn off energy - they could always eat in the car when we were on the road again, and that would keep them occupied for a while.
We discovered that stopping at a McDonalds with an indoor playground was a great option (I favored indoor so we would be in the AC as we were traveling out in the desert). Dh would buy a drink, we'd have our peanut butter sandwiches, and the kids would run all over the playground. Most McD's also have water, so we could refill drink bottles, etc. I'd make a sandwich for the kids to eat once we got back in the car.
In the end, the best tip I have is to remember to enjoy yourself. Remember that you have a general plan in mind, but it's okay to rearrange things. And that will happen when you are traveling with small children. Remembr to take lots of pictures!!
(Check out Antique Mommy's carnival for more travel tips!)