Things have changed since the last round-up I did (need to update that list of software at some point, too.) Anyway, having discovered Aiwa do nice multi-purpose soft cases that have two zipped bag compartments, which can be had for under three quid on eBay, I picked one up and filled it with stuff I find useful.
SD card reader with a 2Gb (micro) SD card, holding portable apps, anti-badware installers and a selection of music, which can be write-protected. I don't understand why this feature is so rare on flash drives these days.
8Gb flash drive with software installers and OS updates via ctupdate.
16Gb (well, 15Gb after formatting) flash drive for transferring files between machines.
Multiple format card reader.
USB 2.0 extension cable with adapters for 5pin mini-usb, hirose mini-usb and printer.
XP Home SP3 OEM, XP Pro SP3 Corp, Vista Retail SP1, Ubuntu Desktop LiveCD, 2000 Pro Select, Offline NT Password & Registry Editor CD. Plus a few blank DVDs/CDs.
Weighs in at about 450g. What I'd really like is an easy way to put most of those CDs onto one DVD and still have them fully bootable, including the recovery consoles, Linux, etc. Sadly no-one seems to have come up with a way to write a boot sector that seamlessly redirects to an ISO or other boot sector.