I was using a tote bag I received as a prize with a lining added. It has a zipper and two inner pockets, and can hold one pen. It has a button to prevent the contents from spilling out. You can also attach a shoulder strap to carry it on your shoulder. The size is 20cm tall, 25cm wide, and 10cm deep. I also have a gray one in a different color for sale, so please take a look.