Tips on Taking the Bumps Out of a Highway Holiday : Driving: Emergency tools and a safety checkup are essential. And bring a picnic lunch and a map of the byways.

WASHINGTON — Probably everyone who takes a driving vacation packs along at least one special item that has become a traditional, even essential part of any trip. I customarily tote two.

The first is a picnic lunch, because I like to drive back roads instead of interstates, and who knows where I might find a cafe when I’m hungry? The other is a detailed sightseeing guide, because I hate to learn too late that I’ve whizzed by something I might have enjoyed.

Not surprisingly, neither of these two items is mentioned in the advice to vacationing motorists offered annually by the American Automobile Assn. and Mobil Travel Guides. These organizations are more concerned with helping travelers avoid the potential hazards of a trip, such as a flat tire, vehicle breakdown or other on-the-road emergencies. Theirs certainly is useful information, which anyone planning a driving vacation should consider. To it, we’ve added some tips of our own, which we think will make the trip more enjoyable.

By far, motoring remains the most popular mode of travel for vacationing Americans. The vast majority of all summer vacation trips this year will be in a private car, van or recreational vehicle, according to the U.S. Travel Data Center in Washington.

Over the years I’ve covered lots of miles in all 50 states, and I remain an enthusiastic motorist for several reasons. Driving vacations are the easiest summer getaways to plan. And they often are the least expensive, particularly if you stick to budget motels and eat modestly.

Preventive maintenance may spare you the hassles of vehicle breakdown on the road, cautions AAA, which advises motorists to have their cars inspected and tires checked before leaving home. “Hot temperatures can be brutal on a poorly maintained automobile,” it says. Check all fluid levels--oil, coolant, windshield washer fluid and battery water. Take a look at windshield wipers, hoses and belts for excessive wear.

But even this doesn’t guarantee something won’t go wrong, AAA adds. It advises packing an emergency supply kit for use in case of a breakdown. The kit should include jumper cables, basic hand tools, flares or reflective warning triangles, a first-aid kit, a flashlight with fresh batteries, a jack, duct tape, gloves, and if you plan to wander off the beaten path, a citizens band radio or cellular phone to call for aid.

Because “a hot day on the side of the road without water or shade can become a motorist’s worst nightmare,” AAA also suggests carrying drinking water and a windshield shade that will reduce heat buildup inside the vehicle.

To help avoid back problems and prevent fatigue, researchers at the University of Vermont make these driving and riding recommendations:

* Take a rest break every 100 miles or so.

* Change your seating posture frequently, especially if you are the driver, simply by readjusting the seat levers. By doing so, you stimulate circulation in your back.

* Don’t unload heavy luggage immediately after driving or riding in a vehicle. If you have been on the road for a long stretch of time, wait an hour before toting the bags to your room.

And these additional suggestions from yours truly:

* Make frequent stops. I’m a sucker for scenic vista points and almost invariably stop. Also, I’m always looking for opportunities for short walks, whether in a town through which I’m passing or in the countryside.

* Limit the number of miles you drive in any day. I try to stay under 200 miles a day, which means about four hours in the car. That’s plenty.

* Stay in distinctive lodgings. One of the joys of a driving trip is the beautiful scenery along the way, which can nourish the spirit. So I try to stay in inns, lodges, ranches or other accommodations that promise good views at the end of the day’s drive.

* Avoid interstates. I like the slow roads that take me through small towns rather than around them. They are part of the America I want to see.

Christopher Reynolds is on assignment.