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)
Free Knit Scrunchies Pattern – Update – Savlabot
NEW - Scrunchies Knitting Pattern - Amanda Berry
How To Knit A Scrunchy 3 Ways! – The Snugglery
free pattern: kestrel scrunchie – Quince & Co.
Free Knit Scrunchie Pattern — CLICKETY STICKS
Knitted scrunchie — Romii
Scrunchie Knitting Pattern, Quick and Inexpensive Gift