*It is always a good idea to pack extra underwear...even if you don't think you'll need them. Because you *absolutely* will need a pair should you forget to pack one. And anything that might save you a trip to Walmart is a very good thing.
*Same goes for children's motrin. If you don't pack it, one of your children will wake up in the middle of the night in your hotel room with a raging headache, and their daddy will have to get dressed and drive for 10 miles just to find a convenience store to purchase some, then you'll spend 15 minutes trying to get the child with the monster headache to swallow a tablet because the only store open at 3am didn't have liquid, and this will eventually end with the child chewing the tablet (to the complete disgust of her mother), finally falling back asleep, and giving that monster headache to her parents. Better yet, just pack the whole medicine cabinet. Can't hurt.
*Even when you're 99% sure that your friends' oh-so wonderful vacation condo will be available for use the week of your vacation...go ahead and have back-up accomodations...just in case. You'll save yourself about 12 hours of frustrating internet searching.
*When your 10-year-old insists that you're "not going the right way to Noodles & Company" please just keep driving rather than confer with him about the "right" way to go. Really, it's just not worth it. He'll get over being wrong and you can console him with some Wisconsin mac and cheese...and maybe a Dr. Pepper.