Avoiding an Odd Couple Odyssey With Friends : Vacations: Before planning a trip with your best buddies, know their quirky habits and spending and sleeping patterns.

Few things are as critical to successful travel as good companions. You may not have the option of leaving behind a grumpy spouse, but when you can pick someone to accompany you on vacation, choose with care. Even best friends may make the worst of travel companions.

A vacation, remember, is not the same as having dinner with the neighbors. Odd personality quirks that can be tolerated for a few hours can loom large when you’re together for days or weeks under stressful circumstances--and minor differences of opinion can fester into grievances.

Once you have found compatible traveling partners, you don’t want to lose them. I’ve run into people who travel together regularly because their interests and habits blend, but who go their separate ways at home. On the other hand, my wife and I are very close friends with a couple with whom we never would travel for more than a day or so. It would kill our friendship.

Probably anybody who has traveled much has a tale of mismatched companions.

Years ago my wife and I, who are frequent travelers, invited a couple from her hometown to join us for a couple of weeks in Europe. We were the experts who would introduce the first-time visitors to a part of the world we like very much. Unknown to us, the husband was the enthusiast pushing for the trip; his wife agreed to come along reluctantly. She thought the cost of the trip could be better spent on furnishing their house. And so, amid the splendor of the Swiss Alps and the whimsy of Copenhagen’s Tivoli Gardens, they quarreled again and again.

My wife and I share a delight for exotic foods, and eating as an adventure is a significant part of a trip for us. So if we travel with others, we want them to like unusual menu choices too.

Good, well-chosen companions can add zest to a holiday. And I say this as someone who, over the years, has become quite comfortable traveling alone, as I often do.

Last spring, my wife and I took another first-timer to Italy for two weeks--my wife’s sister, in fact. As we all recognize, there is something obligatory about traveling with family members--you can’t say no easily. I had no intention of saying no in this case, and as it turned out my sister-in-law, Pam, proved to be a very good companion.

The three of us explored Northern Italy by train for two weeks, which meant we spent a lot of time in railway stations buying tickets in a language none of us speaks. Rather than let my wife and I, the old-timers, assume such everyday travel chores as ticket buying, Pam pitched in to help. And she did so eagerly and without prompting, as a way of getting more involved in Italy.

Based on experiences both good and bad, I’ve compiled a list of qualities to look for in traveling companions--that is, outsiders with whom you agree to travel. Look for someone who:

* Expects to spend about as much or as little as you do on the vacation. Budgetary differences can quickly erupt into bitter arguments. Decide which you will do or agree to compromise 50-50 before you leave home, or don’t travel together.

* Knows and tolerates your personal habits, and whose foibles you are comfortable with. I am an early riser every day of the week.My wife isn’t. So we have worked out a compromise:I run, walk or swim at dawn, and she arises in time to allow us a full day of vacation activities.

* Shares your idea of fun. I travel to learn, which is how I have fun. A day spent idling on a beach is my idea of torture. If I were looking for a travel companion to the Caribbean, for example, it would have to be someone who realized I would spend much of my time exploring back roads and remote villages.

* Enjoys the same tastes in food. I once traveled in Europe with a guy who figured cheapest was best. He carried a guide to budget eateries and refused to dine elsewhere. Once his book steered us to a place that can only be described as a tourist feeding trough. Every 30 minutes, a new group of young American vagabonds--us among them--was seated at communal tables. I stood as much of this as I could and then started eating better on my own.

* Matches you in stamina. My wife and I like to walk, so we spend lots of time exploring cities in this country and abroad on foot. In Paris a few years ago, we met up with an old friend for several days. Invariably, she wanted to get to museums and other attractions using the Metro. We preferred to walk, arguing that there is a lot to see along the way. Ultimately we agreed to walk one way and ride the other.

* Is as adventurous or cautious as you. Once an old friend told me, “I like it when you are along because you’re always willing to do things.” I took this as quite a compliment.

* Can manage quite nicely on their own, when circumstances require.

* Doesn’t leave the dirty work to you. Let my sister-in-law Pam be the guide here. As much as my wife and I enjoy plotting our own sightseeing itineraries, it proved a relief to have Pam take her turn as the instigator of activities. When she was in charge, she led us to places that interested her but that we might have skipped--and vice versa. Everybody learned something more than they might have, which is what you hope for from good companions.

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Times travel writer Christopher Reynolds is on assignment.