How to access files on a USB stick after booting from that USB stick?

Solution 1:

In order to store files on a bootable USB stick with an OS you need to setup persistent storage when you originally create it then each time you boot into the USB OS files and settings from the previous session should be saved. See these instructions on how to accomplish persistent storage on many different Linux distros.

You can also mount the hard drive (on most Linux distros) from the computer that you are using to run the USB OS and store them to a folder on the hard drive. So the next time you boot into the normal computer OS the files should be where you stored them and can grab them whenever you boot into the USB OS. However this option is not portable like the persistent storage option.