Looking for a general term for things one would store on a spool -- thread, string, lanyard, wire, that sort of thing. Things that occur in long lines and will get tangled up if you don't organize them properly.
You might refer to all of those as line, which means
a length of cord, rope, wire, or other material serving a particular purpose
All things that could be stored on a spool have coils. So perhaps the word 'windings' in combination with coils. As in: "Windings, left uncoiled, are hazardous."
For the record, I'm considering using "filament".