Step 1:
This paper is the size of four a4 papers taped together, The large bags are the size of 2x8 a4 papers taped together. Mountain-fold over the 2 purple lines.

Step 8:
Fold over these two lines. Use tape or glue to keep the model flat.

Step 6:
Press these two places flat.

Step 13:
Tape or glue both ends to the bag.

Step 12:
Here a part of step 11 is already done.

Step 11:
Twist both flaps into a rope

Step 10:
Make the same folds on the other flap.

Step 9:
Tape or glue the edges together, see arrows

Step 5:
Here the model is opened again.
The corners indicated by the pink arrows are pulled upwards when you make both folds.

Step 7:
Fold over these two lines.

Origami workshop in a museum

Step 3:
Fold the model in half, then fold over the two outer lines.

Step 2:
This is the other side of the paper.
Fold both edges outwards.

Step 4:
Make the same folds on the other side

Done!
In this video Joost Langeveld shows you how to make the shopping bag: