Description from Knitty.com:

Exact gauge is not important for this project.

Knit lunch bag. The base of this bag is worked back and forth in garter stitch, then stitches are picked up around the circumference of the base, and the bag body is worked in the round. When the bag body is the desired height, some stitches are bound off, and the bag flap is worked back and forth. This easy project is a good introduction to both knitting in the round, and felting!

In addition, the wool is naturally insulating: Even without access to a refrigerator, you can pack a cheese sandwich without the cheese melting by lunchtime.