I don't mean to create a bootable Live USB stick that has some persistent storage, I mean to actually install Ubuntu on a USB stick and be able to boot up from this on any computer.
I've managed to create a bootable Live USB stick that isn't a full-blown installation with my own user account and data and everything, and also managed to install Ubuntu on the USB stick without being able to boot up from the USB stick, but I have not managed to accomplish both at the same time so far.
EDIT: This answer also only gives me the "managed to install Ubuntu on the USB stick without being able to boot up from the USB stick" problem that I have already encountered :(
EDIT 2: And all the answers about using Unetbootin only give me the "bootable Live USB stick that isn't a full-blown installation" that I have also encountered.