Keeping line from unravelling on a fixed spool can be a trial, whether on the reel or in the spares bag. Although you can buy custom bands to secure the line, complete with manufacturers adverts, a cheaper, simpler version is available.
Nip over to Ebay and pick up some towelling type elasticated ponytail bobbles. For the price of one tackle trade band you can have six of these effective retainers and you could colour coordinate your line diameters.
They fit the larger fixed spool reels, 3000 size and upwards depending on the spool design, and unfurl to cover the majority of the line.
As an added bonus they can also be used to tame unruly spare spools of line.
Simple, inexpensive and practical what more could you ask for?