The scarf pattern I started with is the Meandering Rib Scarf. It was knitted with chunky yarn and size 10 1/2 needles which is different from the pattern. But since this is a fly by the seat of your pants type of "How To" it doesn't matter what patten you use or what needles you choose. Be crazy and spontaneous, it might just work even better than you think (that is what happened here).My finished scarf (knitted scrap) was 11"W x 20"L. Along with this you will need scrap yarn and a crochet hook.
Fold rectangle in half, with right sides together and pin up each side.
With crochet hook, start at open edge and single crochet up one edge.
Then, match crocheted seam with pinned seam and execute a squash fold (think origami.) After squash fold, seams will be running along the center front and center back.
Turn over and insert hook into top edge and make a single crochet that pulls the top two stitches from both seams together. Now continue single crochet down other edge. Weave in loose yarn.
Turn right side out and roll up bottom edge.
Add your own crazy additions!
Alternative ideas: Add loop and button for a neck warmer. Fold rectangle in half and seam sides, add handle and you have a bag. With folded rectangle seam one edge and you have a fun elf hat! Share anymore ideas you might have- what can be done with a knitted rectangle? Thinking... thinking....