Everyone carries around a USB drive these days with a variety of utilities, these three have been very useful in the recent past.
CPU-Z - A great utility to find out what kind of memory is installed in a system. This is especially useful when a system is a plain box with out a service tag or serial number. And it's really annoying to open a box only to find the memory is without a label.
Magic Jelly Bean - This little gem has been in my toolbox for a long time. It grabs the key codes for popular software installed on a system (Adobe, VMWare, Office) including the OS. This is very useful if you have a disk, but lost your installation key or have lots of keys and don't know which ones were used on a particular system.
Wireless Key View - And finally, this tool grabs the WPA/WEP wireless key(s) from a Windows system (must be using the built-in Windows wireless utility) when you can't see the actual text or log into your wireless router.
And while you're visiting these sites, check out the other free software they have. You'll have your 32GB thumb drive filled up in no time ;)