1. Start one week before leaving. This doesn't mean get the suitcases packed, but make a list and set some things aside that you will need.
2. Make a list. Include everything. I find that when I am packing I think of other items I need to take and if I don't write it down, I'm likely to forget it. The thing with packing is that there is so much to organize that a list is the only way to go.
3. Take a little extra than you think you need. Take a few extra diapers, a extra change of clothes and a second pair of shoes. You just never know what can happen.
4. Use baggies for traveling. I put lots of things in baggies from my hot chocolate to spoons to napkins to shampoo. The baggies in return can be used for garbage, such as diapers. I also like that it is a little easier to find things if they are contained in a baggie.
5. Anticipate all weather. At least in the Midwest.
6. Don't forget medicine. I always take some Tylenol and Benadryl for my daughter. You just never know. We always carry some ibuprofen for ourselves.
7. Have some cash with you. Sometimes you just need a couple bucks here and there.
8. Pack cooler with lots of ice if traveling long distance.
9. Pack new toys/books or favorite toys that have been out of sight for a while. This will help in the car and to entertain while vacationing.
10. Have easy snacks for the car. Cheerios, raisins, and other things that aren't too crumby.