Toothbrush, passport, clean socks, PDA, Walkman, CDs, laptop, camera, camcorder, pocket recorder, GPS, mobile phone . . . remember the days when all you needed was your Filofax and a couple of ballpens?

These days no self-respecting business traveller leaves home without enough electronic equipment to open a small shop, plus, of course, the associated chargers and a spaghetti of wire that makes an Italian restaurant look under-supplied.

The digital hub of your mobile universe is your laptop. Even this isn't a straightforward choice. Do you, for example, want a tiny, light machine that may require you to buy expensive add-on ports and external drives? Do you want more processing power and hardware, which adds to the weight? Do you want a PC or a Mac?

Those obsessed with travelling light should look at the smallest member of Sony's pretty Vaio family. The snappily named C1VFK is tiny - just under 10in wide and 6in deep, and weighs just 1kg. It also offers Bluetooth wireless technology, which - one day - will be more useful than it is now as a way of wirelessly hooking up to your mobile phone or synchronising with your personal digital assistant (PDA).

More fun is the tiny digital camera it incorporates in its lid: in theory, you could use this for videoconferencing, but might prefer to send back pictures of your sumptuous hotel room.

Mac fans are limited in their choice as the only supplier is Apple itself: the latest iBook is well-equipped with a combination DVD/R and CD-RW drive, Firewire ports and the beautiful OS X operating system, but it is much heavier than many comparable PCs, weighing in at 2.2kg. You may also have more trouble getting support for hooking up to hotels' own high-speed internet access with a Mac.

Go for something with a big hard drive - it is not unreasonable to expect 20GB (and up) of storage space. You will need it if you are going to travel with a digital music player and a digital camera: high-quality picture files, in particular, can consume a lot of space.

Digital cameras come in specifications to suit everyone from someone who just needs to send back low-quality snaps of a site to high grade images for professional photographers. A personal favourite is the Fuji Finepix 6800 Zoom, which offers an output resolution of up to six megapixels and a reasonable amount of control over the settings without moving into the £1,000-and-up price range of the "prosumer" class of cameras such as Fuji's 6900 Zoom and the Canon EOS 1D.

A similar camera to the Fuji 6800 is Sony's DSC-P5 camera, with an effective 3.2 megapixel output. Or you could hang on for Nokia's 7650 mobile phone, due to launch in the second quarter, which will incorporate a tiny digital camera and be able to send the resulting picture back as an enhanced text message.

Many travellers like to listen to music on the move. However, digital music players are often flawed by their limited fixed memory - most offer no more than 64MB, which will give you about about an hour of music, which is not much use on a long-haul flight.

I like Sony's expensive but tiny Network Walkman, which accepts Sony's "Magic Gate" Memory Sticks, available in sizes of up to 128MB. For an initial outlay of about £300 in the UK, the MS9 comes with a 64MB Memory Stick, while adding a 128MB Memory Stick to your shopping cart will put another £200-odd on your bill. However, gym-users will love the fact that it has no moving parts, and therefore will play without "jumping" - however hard you pound the treadmill. Newer Vaio laptops will read Magic Gate Memory Sticks in a dedicated slot without the need to carry the USB cable around, too.

Mac users have the option of the wonderful iPod music player. This is in effect a portable 5GB hard drive with a no-frills interface which can hold up to 1,000 songs at a time. It connects to an iBook (or any other recent Apple computer) via the proprietary Firewire port, offering much a faster transfer than PCs' USB connection. However, it's a surprisingly heavy and chunky piece of kit - and unfortunately for PC users, does not work with any other operating system.

If you can't face dragging your laptop around, you can achieve a lot with a modern PDA. You basically have a choice: the small and elegant Palm operating system, or the powerful but power-hungry and clunky Microsoft Pocket PC OS.

I use a Handspring Visor Prism, a chunky Palm OS machine with a colour screen, with which I can do some limited surfing of the internet, pick up my POP3 e-mail via the IR ports on the Handspring and my Nokia 8890 mobile phone and even write return e-mails via the tiny foldaway portable Targus keyboard that snaps on to the bottom of the PDA.

A good choice for Pocket PC users is the Compaq Ipaq, a powerful machine with additional functionality such as Bluetooth support, which means - in theory - that you could connect up to an office local area network if it were Bluetooth-enabled.

Both the Ipaq and the Handspring are particularly well-equipped with expansion devices. The Visorphone, which plugs neatly into the Handspring's expansion slot, turns the PDA into a fully functional (if large) mobile phone, while the MotionEye module adds limited digital imaging to the machine. The Ipaq has "expansion jackets" - which add to the bulk - including a GPS jacket to help you find your way to your next meeting, and one that allows you to run Powerpoint presentations without resorting to a laptop.

Perhaps the most interesting toys, though, are those that combine two or more functions in one machine. Some are superbly successful, such as Sony's Clie, which, in addition to being a small, light and classy Palm OS-based PDA, is also a Memory Stick music player. Others are less so: Fujifilm's 30i camera is also an MP3 player, but is good at neither function.

Mobile phones offer the most interesting "convergence" possibilities - Motorola's chunky Accompli combines a PDA with a mobile phone plus GPRS functionality. Another, more "grown-up" PDA/mobile phone device is Nokia's Communicator. Although it has all the visual appeal of a house brick, it runs the niche but much-loved Epoc OS on a colour screen and is sturdy and useful piece of kit.

Ericsson's T68 does everything except make tea: it has a colour screen, e-mail functionality, Bluetooth, and comprehensive calendar and contacts applications, though you may think life is too short to get to grips with all its menus.

The oddest-looking device, however, has to be Nokia's 5510 mobile phone. Not for the minimalist, as it would be quite effective as a doorstop, it is nonetheless wonderful for anyone who loves SMS messaging since it has a small but useable keyboard. And, most fun of all, it is also a radio and an MP3 player, though the latter only offers 64MB of space. Who said kids had all the best toys?