By PortableApps.com is a really useful site that I can highly recommend to anybody that has a need to have a collection of applications handy. It's especially handy if you're going to look at somebody's PC and you want to use software that you're familiar with. The Standard version will run from a 512mb USB stick, their Lite version will run from a 256mb USB stick and the totally stripped down Base version will run off a 1.44mb floppy disk. All 3 versions are easily extendable with other applications available from the same site.
I've got a flash drive with most of the apps on. Very handy. Also got firefox portable on it.