** If at all possible, pack each child's clothes in a separate suitcase or small duffle bag. We've found the carry-ons with rollers to be invaluable for our plane trips. The suitcases can double as the child's personal chest of drawers while on the trip. Baby clothes should also be packed in their own separate suitcase, as you can get to it more easily and avoid lost items. If you can't bring a separate suitcase for your baby, put the clothes on top of yours in the suitcase.
** Try to bring wrinkle-resistant clothes that can serve several purposes, and pack clothes in a few basic mix-and-match colors. Bold colors and patterns are more likely to hide stains. Don't forget to bring the stain stick though -- it will save you lots of time and money!
** Resist the holiday urge to bring all new, beautiful clothes and shoes that your child has never worn. You may be surprised to get to your destination (as we did once) and find that: a) the shoes aren't comfortable; and b) all those new clothes either don't fit or aren't ones they want to wear.
** Bring lots of plastic bags for toiletries, liquid medicines, wet diapers, and/or wet bathing suits. If you're really organized, you can pack each day's outfit for your child in its own plastic bag.
** Take a night light, as well as a few of your child's favorite toys or items. Your child will be more secure and comfortable sleeping in a strange place when something familiar's there.
** Here's a great tip for re-packing on the trip: Rather than trying to separate your children's dirty clothes, just turn them inside out. It saves space, and makes dirty clothes easy to spot. If you're traveling by car, bring a large plastic garbage bag and put all the dirty clothes in there. It makes it easy to take them to the laundromat or pop them in the wash when you get home.
** Pack the car when the kids are asleep, or are off doing something else. The packing will go much faster, and you won't have to include all the extras your children suddenly decide they "can't live without".
** Many luggage bags look alike, and can easily be mistaken by holiday travelers rushing from their plane. Try attaching a colorful luggage tag, stickers, or a bright tape to your bag, so you can quickly tell it apart from others. We learned this lesson the hard way on a trip to the beach, and have now equipped all of our bags with brightly name tags in strong plastic cases.