Odd-shaped gifts, running out of wrapping paper, a desire for a reusable package, and limited time are all situations which call for a quick little gift bag.
Wrap the fabric loosely around the item and cut to size, leaving space around all edges.
You need a casing, so turn over about an inch of fabric, iron and stitch down. I cut this with the selvage side on top so don't need to finish the edge. Usually the selvage runs up and down in a piece, but this is just a gift bag and we're going for easy--thus, we get to break the rules.
With the casing stitched, fold the bag in half, right sides together and casing on top. Be sure to start your needle in the seam of your casing, not at the top of the fold; otherwise, you will stitch the casing closed. You want to keep the casing open for the drawstring.
Sew the open side and bottom together. Once the bag is stitched closed, the drawstring will fit better if you notch the casing to be even with the side stitching.
Turn the bag right side out. Then estimate how much cording you need for the drawstring (this is clothesline, but you can use ribbon, fleece, felt, or bulky yarn) like so:
Push the drawstring through the casing (I always use a safety pin to do this). Knot the ends, and you're done.
I remember making this type of bag over and over when I was a child. It's probably the simplest, easiest sewing project there is--it needs no measurement or pattern, is sewn with just a few straight seams, and can be modified as needed: two drawstrings instead of one, tucking in corners to give the bag a flat bottom, piecing fabric like a quilt, making a separate casing from contrasting fabric. You can line it. You can add handles and a pocket so it doubles as a tote afterward. You can appliqué a contrasting star to the front. The above bag is about as fast and basic as it gets, but go ahead and play with it, and see what variations you can come up with. That's what making things is about, isn't it?