Doesn’t the bag look great?
There’s even a short instruction (actually it doesn’t have to be longer ;-)):
They are putting a cardboard into the bag so that the dye don’t bleed through to the back side, then they start to doodle the first item with a black fabric pen (washable!), after this the next item and the rest happens all by itself.
They say that the doodling is completely relaxing and that also children have much fun with it.
A Zentangles bag surely would look wonderful, too ;-)
Links:
Doodle Bags (Kritzeltaschen) (German):
Entry showing the picture
Short instruction
Here at unikatissima: Zentangles