I've built and flown a bunch of streamer-recovery rockets, so I know that there are many different streamer attachment methods used in the kits' directions. My general practice is to use 6" - 12" of cotton or Kevlar string tied to a snap swivel. This provides enough line to wrap around the folded streamer to keep its compact shape in the body tube. The swivel allows me to share streamers between rockets, or to experiment with different streamer materials in a given rocket.
I've never had a burn-through when using the cotton string, and it's way cheaper than Kevlar, btw. I'm sure you'll hear other opinions, but use what works for you. Good luck!