Occasionally, in our travels, we make mistakes.

We take 36 shots of the inside of a lens cap.

We glance away from the scenery and find ourselves walking with a completely strange tour group.

We put bottles of perfume in our suitcases with the caps on almost tight enough.

We forget what the car we rented looks like or where we parked it.

We can't recall the name of the hotel where we called ahead for reservations.

In the course of an introduction we forget our spouse's name.

Normal little mistakes.

It's the bigger ones that need special consideration, the serious ones that make us stand back, shudder and gasp, "What was I thinking?" So many of these, at least for me, seem to involve the same basic error -- unwise purchases -- that they're worth special consideration.

When I was a young man, I went to San Francisco for a weekend.

When you go on a trip, you buy presents for those at home. It's a tradition. So I bought my 4-year-old nephew a set of finger paints.

Good old uncle Bob, right?

Wrong. My sister was very upset. She mentioned that, should I ever do a "thing like that" again, she'd cease speaking to me forever. Since all our lives we had been adversaries, I thought she probably meant it. I swore I'd be good. No more messy toys.

The following year I went to New York. I bought the same nephew a 50-shot water rifle. After all, how much of a mess can a kid make with plain water?

Shudder, gasp, "What was I thinking?"

Not serious? My nephew is 38 years old now. That's a lot of silence.

In Geneva one year, a couple in our tour group fell in love with a cuckoo clock. It had all sorts of hardwood carvings, encircling a dark wood Swiss chalet from which a cuckoo emerged hourly. It had chimes and pine-cone-shaped solid brass counter-weights, weighed 43 pounds and was three feet tall.

Because the price the merchant wanted for crating and shipping seemed excessive, the couple got a bit huffy and said they'd just take it with them on their bus, whereupon the bus driver got a bit huffy, claimed he had been hired to transport people and their luggage, not cuckoo clocks, and refused to touch the thing.

By the end of the tour the husband referred to it as the "albatross" clock. His getting caught -- by his wife -- about to drop it off the ferry on the way back to the United Kingdom almost resulted in an instant divorce.

The couple did not take the same aircraft back to the States as the rest of us. The airline could not quite accept the uncrated "albatross" as a carry-on.

In a later communication the wife mentioned that, though it seemed to awaken her husband every hour, on the hour, the clock was stunning in her living room.

She had, however, been forced into a compromise. Her husband had made her agree to let a local clockmaker inactivate the quarter-hour chime.

Money can also be a dangerous bargain. On our first trip behind the Iron Curtain, our tour guide advised us that the exchange rate on the Polish zloty would be 250 to the dollar.

When the Polish State guide got on the bus at the border, he told us that the Polish government had given him special permission to offer tourists 600 zlotys to the dollar.

He also advised that it might be unwise to buy zlotys on the black market. The word "gulag" appeared a time or two in the advisory.

We all bought zloty in small amounts from the Polish guide.

Outside our hotel, in Warsaw, some of us were approached by Peter Lorre types and offered 800, then 900 and finally a thousand zlotys for an American dollar.

The next morning one of our number confided, somewhat smugly, that he had become "wealthy." The previous evening he had bought a half million zlotys for only $400.

"That's about 1,200 to the dollar. Pretty good, huh?"

There was a long silence at the breakfast table until someone, who had been to Poland before, said, "It'll be interesting to see what you buy with them."

"Well," said the half-millionaire, "I saw some crystal in a shop window at one-twentieth the price it was in West Berlin."

In Warsaw what one sees in shop windows is seldom what one can buy inside. He was told he could order the crystal and would be informed as to when he could pick it up. It would not be long, perhaps only a year or two. Not really so bad when you considered that the average waiting period for a new car in Poland is seven years.

The day before we were to leave the country, the half-millionaire announced that he was going take his losses, accept the government rate and buy dollars with his zloty fortune.

"From whom?" asked our tour guide. "The Polish government does not buy zlotys. It only sells zlotys."

In Venice, off St. Mark's Square, there's a place the tour directors refer to as the glass factory. Each day numerous tour groups are conducted inside, sit down in front of a glass-furnace and have a demonstration of glass-blowing. You tend to get a little over-heated, but it's worth it.

Then the guests are given time to visit the sales rooms and marvel at the wondrous creations of the company's artisans.

My wife Joyce and I have been there twice, and each time the man in the sales room has seemed to have an "accident" while showing some of the glassware.

In front of everyone he tips a tray of thin-stemmed, red wine glasses. They all fall over, banging against each other, and maybe one or two drop to the carpeted floor, yet none of them break.

That simple "accident" invariably astonishes everyone and just as invariably sells a lot of glasses.

The last time we were there, a couple from our tour group really got excited.

"Good lord, Bernard," said the woman, "did you see that?"

The man, as astonished as his wife, nodded. "Should have been broken to smithereens."

"I have just got to have a set of those, Bernard."

Bernard looked at his wife as if she were crazy. "Are you out of your mind? Those are wine glasses."

"No, they're juice glasses and I've just got to have them."

While Bernard's wife bought the glasses and arranged for the company to ship them, Joyce and I talked to him.

"What's so crazy about buying wine glasses?" Joyce asked. "They're beautiful."

"What are we going to do with 'em? Up till two years ago I did my drinking out of a brown paper bag." He shook his head. "Since I went on the wagon we don't even hang around people unless they've got blue noses. I'm A.A. She's Al-Anon and a dozen other anti-drinking groups."

"Bernard," said his wife. "We'll use them for our orange juice. I just can't not buy them."

She bought them. The glass factory was happy to ship them.

Eight months later Bernard dropped us a line. The orange juice idea hadn't worked out too well. The first morning they'd used them, they'd sat down at the breakfast table to a bright morning sun streaming through the kitchen window. The only trouble was, when the sun hit those red glasses, it made whatever was inside look like blood.

His wife had decided to relegate the glasses to a position of honor on a kitchen shelf but lately had announced that they tended to make her whole kitchen look tacky so she was thinking about redecorating.

Knowing the redecorating would spread through the house like wildfire, Bernard was thinking of "accidentally" putting the glasses to the test one more time. There was a Mexican tile floor in the kitchen.

I have my own particular travel-purchase failing. At about the first duty-free shop we come to on any trip we take, I buy a bottle of my favorite English sherry. It's just such a bargain and I like a little before dinner.

Of course I have to be extra careful with my hand luggage until it's all gone, but what the heck, it's the price you pay and wine stains aren't really all that hard to get out anyway.

But the fact that my hand luggage has taken to sticking to the floor is beginning to get to me. And I know the ants and the fruit flies that seem to show up wherever we go is beginning to ... if you'll pardon the expression ... bug Joyce. Bob O'Sullivan, a retired Los Angeles sheriff's lieutenant, travels extensively with his wife.