This is pretty standard stuff, if you’re reading this, it’s likely you already know it. Like I said, I’m using a Macbook Air, so there’s two steps to this process: creating a bootable flash drive with the Ubuntu image, and the actual installation. Scouring the web, there’s not that many resources indicating how, or if this is even possible.
Recently I was trying to find a way to run Ubuntu off an SD card, so that I could use Linux on my Macbook Air (I’d have dual booted, but my Air has the 128GB SSD, which doesn’t leave much space after partitioning).