Traditionally, by Japanese regulations, my ideal size bento box is about 500ml, and S-chan’s is 900ml, but I’m a poor college student, so I just use what I have. I bought these metal containers at Sams Club earlier in 2007. They came in a set with other items, but these had great lock-on lids. For a little color, I folded up a piece of fabric on the base of mine. It also cuts back on the washing of the container itself if something spills. I can just wash the container with soap and water, and wash the fabric with the laundry. I recently ordered a bento box and supplies on e-bay. I fell pray to their expensive shipping :[.
Another thing I wanted to say is that in Japan, the portions of food have guidelines, too ( grain dishes make up 3 parts, veggies 2 parts, fish and meats 1 part, and milk/dairy and fruits are only to be used occasionally ). While in my later bentos, I do try to follow these guidelines, I mostly use what I have and like to eat. I don’t eat a lot in one sitting though, so the portions are still pretty moderate. For more information about picking your right size bento box, and the guidelines for the food that goes in them, visit Lunch in a Box’s Guideline Page (http://lunchinabox.net/2007/03/07/guide-to-choosing-the-right-size-bento-box/). She always has good ideas for bentos, and how to pack them quickly.