Pack light. Most of the places you are going have washer and dryer facilities. Spend the kids' nap time doing a load of laundry here or there to save room in the car for comfort. Pack each child's bag to last 3 days with 2 extra t-shirts for spills. Alternatively pack light clothes with one warm sweatshirt and pants set.
Choose the most organized person and the best stuffer for the task of packing the car. Husbands and wives can experience a battle of the sexes while packing a car. One of you needs to humbly admit that the other is better at packing the car, while one is better at carrying all the baggage out to the car. Agree to the social order in your home and stick to it. Don't interfere.
Find small lunch box-sized bags for the kids' toys. Each child should pack their own "fun" bag with whatever favorite toys, books and markers fit. Place this bag in the child's seat. They won't need all their toys. This is a vacation, not a relocation.
Consider buying a roof rack, roof storage or a trailer for added space. As the car drives down the road, the doors, windows, ceilings and large baggage will begin to close in on you. The kids will pull all the toys out, scatter them across the car, and your spouse will toss snack trash everywhere. Avoid the closing-in effect by removing the larger items. Place suitcases, strollers, bikes and other large items outside the vehicle. Rent a UHaul trailer if need be.
Use your hidden space. Use the space under the seats for portable cribs, medicine chests, blankets, pillows and towels. Put snacks in the center console or in the consoles along the sides of the car.
Lay out all the bags and extras for the trip on the lawn and then plan the packing. This is as much a logic puzzle as ever. Think it out and be willing to admit something isn't working. Start over if need be. Put the most important stuff in an open and easily accessible location. Enjoy the trip.
