My favorite level line spools...
Rigged and Ready
I haven't understood why these spools haven't received more publicity. Granted, they aren't as high tech or fancy as other spools, and they aren't as durable. Further, they won't hold many furled lines. What they excel at, however, is holding level fluorocarbon lines.
Do a search at a large online auction site for "foam spools" and you will get many listings for these foam spools with a faux wood grain. Choose the cheapest, they are all the same, but aim for the ones with the pop out slots in the body. Frankly, that's no guarantee that's what you will get (I've gotten ones with no slots, with one slot, and with two slots, all from the same listing) but it might increase your odds. All will work, but the ones with the slot to hold your fly works just a bit better.
Anyway, they are really cheap and decent looking. If the only last a season, OK. Mine are well into their second season with little sign of wear. They accept sharpie ink well so there's no reason not to write the line size and length on them.
Best of all, they are light, small, and soft, making them absolutely perfect for stringing on a lanyard or the cross brace on the BW Sports Tippet Pouch as shown in the image above. All of those lines are rigged and ready to go and get used even more than the furled lines on "Stewart Stars" in the pouches inside simply because they are readily accessible.
I still carry the small Meiho or the gold and brown Oni spool a good friend brought back from Japan for me - I use it for quickly winding the line to move to another spot, but truthfully it really doesn't take much more time to simply rewind the line on the foam spool.
I haven't done extensive testing, but the only line I wasn't able to fit on the spool was a No. 4.5 21' line. The limit is somewhere around there.