Recently, I did some modifications to my Surly Steamroller. I put on a bullhorn handlebar from my vintage MTB and added a rear brake. My Steamroller is fixed gear now, and I don't really need the rear brake, but I'm planning to add a freewheel for the winter.
Steamroller doesn't have any cable guides for a rear brake, and I started figuring out the best way to attach the cable to the top tube. I looked at some clamps, zip ties and top tube protectors. Then I decided to use paracord as the top tube protector and to hold the cable in place. Paracord is really durable and I use it all the time when I'm camping and pitch my tarp for the night.
It's still a bit of a work in progress, but I'm quite pleased with the result. The Internet is full of guides how to make all kinds of things from paracord, and I picked up a simple weave that someone recommended as a wrap for axes, hiking poles and what not. I think it looks pretty nice :) It adds a nice and soft, almost organic feel to the bike.
I bought a reflective paracord for this purpose. In total there's about 11m of paracord. I could easily cut out a few meters if I need extra cord for pitching my tarp, or if I need to replace luggage straps while I'm touring. It's nice to have some extra paracord for backup and this is a convenient way to always carry it with you.