Best way to continually add to my backup memory stick

Backup threads are always fun to read.

The main thing has already been said. Keep backup on several separate drives and one offsite.

Online backups as Network drive or secondary disk on the computer do not mean a thing if you get a ransomware that encrypt all files on all disks/network drives that is connected.
This is when the offline backup will save your butt.
Keeping several offline disks at home dont mean a thing if your house is burning down to ashes.. No drive survives those temperatures...
This is when your offsite backup will save your butt.

also what to backup.. personal files.. some can never be restored as photos and other things. This is prio 1.
Movies or music can be downloaded again and can be skipped if you dont have enough backup space and if you have, then prio 2.
Your OS is the lowest priority as its easy to install it again. So this is prio 3.

Kind of Media..
DVD disk is pretty good protection against long term bit-rot.. Only a ZFS pool can beat a DVD in bit-rot protection.
Downside is that DVD disks are a bit sensitive about how you store them
SSD is fine as one of several medias. But as already pointed out.. SSD is not for long time storage if they never get plugged in and running trim(or what they call it on windows)
HDD is really good for backups, as you dont need performance on backups as you dont use-use it. The downside is.. HDD is really sensitive against external hits if they are in use.. Just hitting your hand hard in the desk and the disk is on the other side of the desk can make the heads touch the disks inside and you soon have a dying disk on your hand.. So on external disks with HDD should have a sticker saying.. handle with care.
This drives is also important to shut down correct so the heads park before it shuts down. (modern drives often have a protection if power goes out the head will return to park by it self)
When a HDD is off and the heads are parked, they can stand quite a lot of abuse..
Dropping a laptop in the ground from the table when its totally shut down, might break the laptop, but in most cases, the HDD drive is still okay.
Hitting the keyboard in frustration when gaming while the laptop is on will damage a HDD. (Nowadays laptops dont have a HDD, but the principle of a HDD on VS off)
USB-sticks or SD-cards can be acceptable as temporary solution while you solving better solution... (everything is better then nothing)
But as a long term solution they are a bad choice as they are unreliable. But if you have several other good backups, then you can have it as an extra backup.

The evil of bit-rot is seldom really noticed by normal users.. but i bet almost everyone of you have seen it sometime.. either on your ow photos or online pictures when a photo get distorted by a bit has flipped from 0 to 1 or 1 to a 0.. Most people just notice it but dont know why.. this is most often caused by bit-rot that is a word that almost sounds as a myth.

A cheap non-technical protection against photos getting distorted by bit-rot, is to just make duplicate of the same photo folder on the same drive.
If you have 1000 photos and you have them times 3.. say you get a bit flipping on a photo and the photo get distorted.. then you still have a copy of that photo and that bad photo will not get overwritten to another backup that has a healthy photo on the secondary backup disk.
If you have photo folders you never change.. say you store it by year. Then you can do a checksum of the folder and its content.. and on backup you can recheck the checksum.. if its changed.. then a photo has changed. And you can switch the bad against a good from the twin folders.

So my minimum recommendation of important personal files is 1+1+1 .... On the device,.... Offline on an external device... and an offsite device. (cloud or an external drive in another location in another building.)

Having more then three is even better.. But that is the minimum


And as stated above.. it is most common two kind of people.. those who has lost data.... and those who will...
and the exception of that rule is those who listen before it was to late.

And to answer someones thought.. Yes i have lost data.
I lost a whole server setup that had two separate raid pools and an online backup (late 90's).... a lightening strike fried the server, the backup server and two computers.
So i learned, that offline backups is darn important.

I have requested that this post is closed, again I thank all who replied