Some distributions of the open-source operating system are bloated, but Puppy Linux, Knoppix, SLAX, NimbleX, and -- yes -- Damn Small Linux will get you up and running fast.
The tricky part is trying to have the OS on your USB memory stick to be able to boot both natively and in a virtual machine. But it can be done. And that's what makes QEMU-Puppy unique.
QEMU-Puppy is an OS and a set of applications on a USB memory stick. This OS can be booted natively or on top of another already installed OS. Just borrow a PC, boot your own environment, and return the PC unaffected.