Thanks for the suggestions. I should have thought out what I wanted a bit better, though your posts are helping me do that. I occasionally use the USB key at college and the public library. I'm not really expecting industrial-strength security. I want to (1) prevent average users accessing payware programs on my USB key, (2) prevent same accessing certain files, and (3) should I lose the key, or forget and leave it behind, plugged into a machine (mine are all on cables, so they're more obvious than usual), then no-one, not even a sysadmin (who hadn't already sniffed the password) could access any secure area. That seems to mean I'd be better off with a TrueCrypt-type secure container to stop (1) and (3) while still making the programs accessible to me. For (2) I could use AxCrypt or equivalent, but even then it would (probably) be a pain while doing things like digital photography evening class where I want to access lots of files, so an encrypted container would still be best. Ideally it would lock itself after a given period of inactivity.
I suppose I should add the obvious - I don't usually have admin rights on the PCs I would in these situations be using.
Like superboyac I use RoboForm, and KeePass, and one of my MemPad files is also encrypted using Windows' built-in system. I could leave those outside the container.
Found two more not mentioned above: Wondershare USB Drive Encryption
. I don't know anything about them.
I notice that some encryption programs are fairly expensive. The ones that have free and payware versions seem to limit the container size in the free version as an incentive to upgrade. Rohos, for example, is 2GB. But that seems quite a bit on a USB drive which isn't enormous anyway.