This knitting bag is made in Tunisian crochet, a wave stitch alternated with a basic stitch. The waves seemed appropriate for the blues and grays I used and the Tunisian crochet makes for a sturdy bag.

This is a written pattern with detailed information about stitch pattern and bag assembly.

There is now a German version of the pattern available, thanks to cooltyson.

Finished measurements: 18.9 x 9.1 x 3.1 inches (48 x 23 x 8 cm).
Yarn: I’ve made the bag with handspun yarn, but you can use any DK yarn as a substitute. I’ve sampled with Rowan Wool Cotton and obtained correct gauge.
The whole project required 593 yards (542 meters) of a variegated gray or any other color you want to use as your basic color and 237 yards (217 meters) of one or more colors for the waves.
Make sure you have enough yarn, the numbers are what I used and therefore approximates. Different yarn may require different yardage and your personal way of crocheting matters as well.
Crochet hook: E (3.5 mm) Tunisian/Afghan hook or any size to obtain correct gauge.
Gauge: 20 Tss and 20 rows are 4 inches (10 cm) and 21 Tss/Tws and 16 rows are 4 inches (10 cm), both using a size E (3.5 mm) hook. Use any size hook to obtain specified gauge.
Additional: 2 aluminum (or plastic or wood) strips of 18.7 x 1.2 x 0.12 inches (47.5 x 3 x 0.3 cm) for reinforcement.