Some caveman discovered fire. Stanley discovered Livingstone. And I discovered the inflatable pillow. Others may leap forward to stake their claims, but I insist on taking credit. It came about like this.

It was the middle of the night in the crowded compartment of a European train. Foolishly I had neglected to book a couchette . Grizzled peasants sitting on either side of me were sound asleep and upright. I couldn't manage it. The seats were rock-hard and no matter how I readjusted myself I couldn't get comfortable.

I tried my purse under my head, my canvas tote-bag rolled up, a book, a jacket, a sweater. What I needed, I thought crossly to myself, is a cushion I can blow up when I need it. Then I wondered if such a thing existed, vowing to search it out on my return home -- though at that dispirited moment, in my narrow space on that miserable seat, home seemed very far away.

So I wrote my idea down. And the next day, sprawled on the bed of a hotel room, I began to make a list. "Inflatable pillow" went at the top. After it came a column of other items I had often missed on trips, small things the lack of which had made itself felt at one time or another: a bottle opener, a flashlight, a collapsible drinking-cup, folding scissors (or a Swiss-Army knife), Band-aids, Cutter's lotion (or other insect repellent), sufficient packs of paper tissue, transparent tape, and the kind of raincoat that squishes down so you can hold it in your hand.

If this seems like the sort of list parents foist on kids for their first overnight excursion, it is. Parents, after all, know best. Because my mother gave them to me once, I've been traveling ever since with a tiny portable alarm clock and a sewing-kit, and I've never regretted the space they took. On the contrary, I've come to savor the charms of being my own Jeeves.

As it turned out, inflatable pillows most definitely exist. They can be purchased at camping supply stores for around $5.

I bought one. Then I wondered how I had ever managed to do without it. Since then it has gone with me on trains and planes (their pillows don't have much propping power), in cars and buses, and to the beach (it is waterproof).

The best test came when I sang the pillow's praises to a couple of friends about to spend a month in Africa. They each bought one and came back as converts thanking me profusely.

If there is a point to this story it is this: Make a note to yourself whenever you think of something that you can use, that you never knew you wanted but suddenly find yourself needing . Not all gadgets are just manifestations of conspicuous consumption; they can be worthy investments. And you might "discover" your own inflatable pillow.

This advice holds true whether for travel or for daily life. Not everyone gets to go first-class, but sometimes a small expenditure of forethought can turn a chair into a stateroom . . . or almost.