I wrote a free pattern for a scrunchie knitted either with 2mm, 3mm or 4mm double pointed needles and some yarn leftovers. You can find the pattern on ravelry (link in comments)
How To Knit A Scrunchie Onto A Hair Tie - plus a little knitting chat - YouTube
Ravelry: Bohemian Scrunchie 1 pattern by Hawre Gyth
Free Knit Scrunchies Pattern – Update – Savlabot
Scrunchie
Scrunchie Knitting Pattern, Quick and Inexpensive Gift