Easiest Linux on a USB memory stick?

Because I’m melancholic, retro-active, and slightly crazy I’ve been playing around with the idea of putting Linux on a USB memory stick, loading it up with emulators for old computers, and creating a menu so you can choose what computer to boot into (VIC-20, Atari 800, Apple ][, etc). I’m having trouble figuring out what the easiest approach is.

I’m used to Gentoo and, to a lesser extent, Kubuntu so I’d need a distribution that would be easy to update and install applications to.

Does anyone have any suggestions for this? What I’ve found so far seems to be a bit too minimalistic for my skill level.