I would like to try out different Linux distros on the go using a USB flash drive.
Is it possible to install multiple Linux OSes on a single USB drive?
There are several options available
Option 1: MultiBootUSB
You could try MultiBootUSB downloadable here
Option 2: XBoot
You could try XBoot, it has considerably more documentation that MultiUSBBoot, although not really needed it's nice to know it's there, it's downloadable Here
Option 3: YUMI
Downloadable here - I don't have much experience with this tool, so I'm not going to say anything about it.
For your consideration, there is a great MakeUseOf article on this topic, located here