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)
Ravelry: Spectacular Scrunchie pattern by Sarah M. Goodwin
Free Knit Scrunchies Pattern – Update – Savlabot
PATTERN the Wavelet Scrunchie DIGITAL DOWNLOAD Knit - Etsy Israel
How to knit Scrunchies:Part 1 - YouTube
Hair Accessory Knitting Patterns - In the Loop Knitting