Just back up files to a cloud service. Dropbox, Google drive, etc.
Or use a USB. You can get a 64GB usb for cheap.
How large are the needed files total?
You didn’t tell me that I needed a high speed USB, I got a Cheeto 128 G USB, and it took almost 7 hours to download the backup through “time Machine’”. Now I’ve got the upgrade for El Capitan loading.to the “Ole” Mac. We shall see if it was worth the trouble.