Tubular tape can be purchased from most climbing shops off the real for £2 or less per metre. You can also purchase 4m (newer models 5m) of Palm tubular tape for around £14 from most kayak shops!
I carry a 5-metre length of 25mm tubular tape for use in rescue situations, lowering boats etc.
My 5m tape rolls into a coil with a diameter similar to a CD/DVD disk. It can be used as a short throw line, tied into a sling around a tree or even turned into a make shift sit harness. The Palm version is supplied with a stitched in loop which makes adding a carabiner into the system really easy.
Tape should be tied using a tape knot (aka a water knot) to prevent any slippage – click here to see how to tie the water knot.