If you're new to knitting socks toe-up, you've probably heard that one of the challenges is making the bindoff stretchy enough so it's not actually binding.
My go to method for a stretchy bind off is the decrease bind off. It's simple to execute, uses the working yarn (so no worries about running out of yarn with three stitches to go), and creates a pretty chain along the top.
BTW, this bindoff is equally great for binding off the hem of a top-down sweater or around a neckline.
|

setup step 1: k1
|

setup step 2: k1
|
|

setup step 3: return both sts to left-hand needle
|

setup step 4: k2tog tbl
|
|

step 5: k1
|

step 6: return both sts to left-hand needle and k2tog tbl
|

when you're done, you're left with a stretchy chain of sts along the top

told you it was stretchy!

the chain looks so pretty when worked in a handpainted yarn