Here is a selection of shock cords and harnesses for your parachute / recovery system.
You can't go too wrong here with whatever you choose to use, although we quite like a long piece of Kevlar cord or tubular nylon with sewn loops. You'll need to setup a good secure system to attach this to your rocket.
Smaller rockets can use systems as simple as gluing it to the air frame, mid and higher power rockets tend to use bulk heads with eye hooks, or motor mounts with secure attachments built in.