Idea to respool your fishing reels while on the water.
Get a tarp bungie and a carabiner
Maybe about a 6” bungee. You can thread whatever spool you want on the bungee. Use carabiner to attach to seat post by wrapping bungee around and snapping carabiner to bungee cord. Casting reel spools can be spool edge on dispensing line off the top (clip carabiner on loop end around post to ball end) and have tension as well. Spinning spools can be held to allow line to come off clockwise or counterclockwise (spool held by ball, carabiner clipped to cord around post).
Problem solved for less than $5 and stores more neatly than anything you’ll buy.