I came up with a simple way to hold the few loose spools of filament that do not have their own box. 

This is also a good option if you need to carry multiple spools to different locations if you have printers in different places. 

This design is fully modular. The base and the handle itself is enough for roughly one 1KG spool with a little room to spare. Then i made barrel pieces to screw in the middle to increase the number of spools this is able to hold. 

I am working on a method of turn this into a multiple spool holder with legs that I can use for the Prusa MMU3 when it is released for the MK4. However, this will come later, because I am still brainstorming and testing.