I fall into the just in case bunch myself. I do have a bunch of extra stuff since I started building Nicosticks. Some are 14500 battery boxes and a few are wall wort 4.5 volt plugins that work on some atties that just dont work on 3.6 batts. I still have my NPro's that I fist started on and they are working well on boxmods, a couple of 510 mods that I usually use 306's on and a couple of 401 mods that are my main vape. Let's face it used atties aren' worth much at all but bad things happen.
I only had 2 401's when one died, next day I dropped the other one into my easy chair and the button was pressed. Melted the cart clean off and also the end of the boxmod. It took seven days to get a few replacements, one died first day and one shorts out the battery. The supplier said he would replace the dead one but two weeks later, no atty. I got more elsewhere that were better anyway, but you just never know when you may need your old stuff.