As a painfully frequent traveler, I carry an assortment of vital accessories in the bag that fits under airline seats. About three years ago, the folks at the gadget blog Gizmodo asked me for a posting on what was actually in that gadget bag. Here’s that old report.

A lot has changed, but a surprising number of items are the same or are updated versions of what I used to carry. At left is a photo of (most of) the contents of the bag.

Herewith, what I carry and why:

The Bag: It’s an old Tumi carry-on bag, just the right size with the right array of pockets and compartments. Amazingly, Tumi doesn’t make this model anymore, and has nothing else with this ideal combination of features and size. I have two of these bags, having bought a spare at a huge discount when Tumi discontinued the model. Once a year or so take one of them to a local shoe and luggage repair shop for an overhaul — fix the zippers, patch frayed areas, etc. A friend told me he had the exact same bag and sent it back to Tumi for repair, but was refused service because it was no longer in the product line. Tumi gets my corporate-doofus award for that kind of policy.

Personal Computer: It’s a 15-inch MacBook Pro, with an extra battery and power brick plus the DC power supply that works on airplanes. I believe Apple hit the bulls-eye with this model, an almost ideal combination of power and elegance. Sometimes I worry how much of my professional existence is in this machine.

Backup: That worry explains why I also carry an 160GB backup drive, the same size as the one in the computer. It’s an OWC Mercury On-The-Go portable drive. I back up regularly to this drive (and another at home), and it’s a good thing. On a recent trip to Finland, I had an accident that wrecked my computer’s hard disk. Because I carry around a clone of the internal drive, I was able to save myself from some major-league woes. (More about that here.)

Modular Carrying Case: On planes I carry my Mac double-wrapped, in a sense. I put the computer in a padded, ballistic-nylon “sleevecase” from WaterField Designs in San Francisco. The sleevecase then goes into a carry-on bag that adds further protection. Once I get there, I pull out the sleevecase and attach a padded shoulder strap and piggy-back bag that holds my power supply plus a notebook (analog), digital camera, a couple of cables and other small items. In effect, I end up with a carry bag inside the carry bag, for protection and fo be able to leave the big bag in the hotel instead of schlepping it around.

Phone/PDA: The Treo 680 is my current favorite phone/PDA combo. I’ve installed a bunch of third-party software on the thing, including a FreeCell game for emergency boredom fixes. I carry the Treo I use a padded camera pouch that attaches to my belt. I also have a retractable sync and cable/charger thingie, which saves lots of room and is vastly more convenient. This phone could be on the way out; I’ve been playing with Nokia N95, which is an astonishing technical achievement and could replace not just the phone but also my digital camera (discussed below). The Nokia doesn’t have a full keyboard, the single most important missing item. It is otherwise fantastic, as I’ll be discussing in an upcoming post.

Assortment of other cables and tools including: Retractable RJ-11 phone, RJ-45 Ethernet, USB and Firewire connectors, plus a worldwide power adapter (pictured left) that includes a USB port to charge external devices without having to plug them into the computer.. Back in the analog modem days I carried a small kit that included alligator clips and wire strippers, which enabled me to hot-wire just about any hotel phone system. Thank goodness that’s no longer necessary, at least in the places where I travel.

Headphones: For me it’s no contest, even at the cost of taking up too much space in the bag. The Bose QuietComfort 2 noise reduction headphones are utterly essential carry-on gear these days. There’s a new, smaller and more expensive model, but I’m happy enough with the ones I have. Someone, somewhere is going to beat Bose at this, but I haven’t heard anything better. Note: I also carry an adapter that lets these headphones work with my Treo (which has become my portable music player).

Camera: The Treo takes (barely) competent snapshots and videos. But I also carry one of Panasonic’s Lumix digital cameras, the DMC-FX01 model. The pocket-sized 6-megapixel camera has a 28mm wide-angle lens, 3X optical zoom, more than competent video (for its size) and a host of other features that, for me, makes it a smart choice for my routine needs.

Other: Extra batteries, USB adapter for various device memory cards to download pictures and transfer files. Also, various notebooks, pens, tissues, anti-bacterial hand-wipes, decongestant nose spray (essential if you get a cold and fly) and other basic remedies and vitamins. And — this is crucial — a book; I never know when I might be waiting in line, and it’s always useful to have something to read.

What I don’t carry: An iPod. I love the iPod, and especially love the Nano. But I have a 4GB SD card in my Treo. You can hold a heck of a lot of music in 4GB, and the Treo battery hardly notices the drain even on cross-country flights. Since I’m carrying all my digital music anyway in the Mac, it’s not all that hard to move a few albums to the Treo before or during a trip. I lose some convenience in one way but gain a lot in another.

An occasional hassle: Airport security. Every now and then, a security crew unpacks the entire bag, given the amount of electronic gear, to take a closer look. I’ve had to explain what the external disk drive was — and, once, even plug it into the computer and mount the drive image in order to persuade one especially paranoid person at London’s Heathrow airport (which has become a destination to avoid) that the disk wasn’t dangerous.

So that’s my story. Now it’s your turn.

What am I missing in my carry-on world? What do you carry, and why?