If you don't have a computer (psst, a laptop is a computer
), you can still back things up.
You can back up many files to a google account or other cloud based account. Just make sure you check the account, from a different device and not the one you are uploading from, when you believe the upload is done and before you do the reset. The reason for this is 'sometimes' the backups don't go through. Either in full or in part. Then if you have already reset the device, you lose what wasn't backed up. So it is always best to check the backed up data from a different device to be sure it is there.
Also, make sure you remove the SD card from the device before doing the reset.