I like to carry basic supplies with me all the time but I like to keep my purse as light as possible. I discovered an inexpensive photo album/brag book works well for me. I found mine at Joann's Fabrics and Crafts for 99 cents. I keep finished tiles in the front of the book and blank ones in the back. My pen clips right to it. This means I also have finished pieces ready to show to people when they ask what a zentangle is.
Sometimes I am so pleased with a piece that I want to frame it. When I was at Michaels Crafts this morning I found a four pack of frames for $9.99. They included the glass and mats too. (Not the highest of quality - but I can always upgrade later.) Square frames can be hard to find, so I'm always looking.
Finally I found Michaels also carried the display cubes. Another tangler found them and posted the info so off I went. I searched the store over and over. Finally I asked for help. When she found them for me, they were on the very top shelf and we needed to find a ladder! But they are only $2.99. Just examine them carefully when you buy them. If they were ever dropped they may have cracks.