I carry a yellow floppy (my "GoldCard") in my shirt pocket.  On it is a collection of all the must-have utilities that I've used for years on DOS and Windows.

I also used to have a ZipDisk of stuff that followed me around, along with a portable ZipDrive.  More recently, I've started carrying a mini-CD (210MB) in that same pocket.  It has the contents of the GoldCard floppy, along with the files needed to install CygWin.

Another mini-CD has every Windows internet tool that I'm likely to need when I show up at a client's place, along with a number of language interpreters and compilers (and, yes, an assembler).

It's all well and good to have one's desktop or laptop fully loaded, but when you show up at someone's workstation and it's set to "MaximumLame" and they're on dialup, you need to be able to function.

It's been nearly a year since I last had to use the yellow floppy.  Everyone since then has had a CD-ROM drive of some sort.  The floppy is about to be retired.  It will be replaced with a pair of mini-CDs that take up about the same pocket space.  One is bootable, the other is jammed with the software equivalent of pliers, spanners ("wrenches" West of the pond), screwdrivers, hammers (gold and otherwise), and drills.

I haven't had the nerve to switch over to USB flash drives yet.  But that's probably coming.

Did you know that everything needed to install Win9x fits on a mini-CD?  I'm looking to configure a BSD or Linux mini-CD for the same purpose.  When I have time.  Yeah, right.

''I'm looking to configure a BSD or Linux mini-CD''

It's already been done. Lots of them. See http://www.frozentech.com/content/livecd.php?sort=&showonly= for a few dozen :)

''I chose a USB flash drive over a mini CD because of lingering doubts over CD drives' ability to read them (based on some chewed-up CDs from the mid 1990s).  Is this no longer a problem on arbitrary CD-ROM drives a client sites?''
* It's only a problem when the drive is of type "slot" rather than type "tray" and for those moments I have to go back out to the car and dig around.  USB will become more attractive when more BIOSes know how to boot from them.