This is a very simple and easy to make bag dispenser. All you need to know is:
chain
sc
sc in back loops only
hdc
dc
slip stitch.

It’s also very easy to adjust the size of the bag by making the beginning ribbing rows shorter or longer before joining into a circle, and the length shorter or longer by crocheting more or less rounds.

I’ve made several of these in various types of yarns, and found that plain old big box acrylic holds its shape and wears best. This can be made with just one of those big box yarn skeins, and there will be yarn left over.

This particular sample shown used plain old Red Heart Super Saver, about 2/3 of a 7 oz skein.