Using the end of a spool I've seen several Q&As on recycling and reusing plastic from failed prints, but what have you done with the last few meters of filament? I've been keeping the ends of PLA (or sections I needed to cut) to maybe use for friction welding pieces together, but I only need so much for that. I've considered just shoving the last bit in the tube and using a new roll to push it through (so long as retractions aren't necessary). This is especially a concern for more exotic filaments where friction welding isn't useful and the price is higher for that 1m section (something like Copperfill). Note: I have a Bowden extruder. I imagine this is less of an issue with DD extruders.

The welding option is only appropriate if you have the tool needed for it, the lighter welding is really hard to do and if your printer allows it you could just watch for the moment the spool runs out and push the new filament as the last of the previous one gets extruded, that's what I used to do on my bowden extruder reprap and apart from a really negligible retraction problem on one layer it just works

Or you could go the cool way:

* Use the last of the filament for friction/iron welding to fix or glue 3D printed parts together
* Use it as regular filament with a 3D printer pen to fix 3D printed parts
* "Use it for pin/studs/rivets/hinges in prints." as tjb1 said
* Stock it with your failed/ waste 3D printed parts and use them in a recyclebot later to make new filament or simply melt it in an oven to make plastic boards/injection molding material
* Throw it away but that would be a waste over time