Panty hose, orphaned socks, and bungee cords are among the things that can be used as plant ties. Twist ties, both paper and rubber coated, and plastic tape are labeled as "Plant Ties" and are available in stores. Also available in stores are hair clips, roller clips, and other unconventional items that work equally well.
After a stay in the hospital, I found another secondary-use item: the tourniquets used to draw blood. New hospital rules for the prevention of infection keep items that enter a room from leaving the room. I was able to "collect" quite a few tourniquets, with blessings from the staff, to use to tie up my plants.
So look around for the unconventional. These items often are tossed away after use and are free for the taking.