Given that I have Mavic Ksyriums which require non-standard spokes, I've lately been very conscious of the fact that breaking a spoke means I can't just walk into any nearby bikeshop and get it replaced. They're unlikely to stock them. So I decided to order a few spares and carry them with me on my rides. I guess this is the price one pays for "one of dem new-fangled wheelie-thingies". I also have to carry along the Mavic spoke tools in my seatbag. However, I couldn't think of a convenient and elegant spot to carry the spokes.
I know many people who do carry spares end up taping them to their seatstay. This works pretty well for standard spokes but Ksyrium spokes have large round ends and the nipple is captive which doesn't lend itself to making the spokes lay nice and flat against a surface.
So after much thinking, I decided that the best place to stow my spokes is in my seatpost. The problem is that the seatpost is shorter than the spokes and the spokes are of course much thinner than the seatpost. How was I to keep them in place? I could have taped them to the inside of the seatpost but I know that over time, the adhesive is likely to degrade and I really didn't want a bunch of spokes floating around at the bottom of my seat-tube. The solution was to make a plug. I decided to wrap the spokes with some old pieces of innertube. The rubber of the innertube would be enough resistance to act as a plug and has the added benefit of keeping the spokes from rattling around.