Just trying to answer a few comments.
Best results I have had for Asian groceries & bento supplies:
Asian World Market at Legacy and Central - This is the big new grocery store between Central & Chase Oaks off of Legacy. It's big, bright and very clean. Great selection, especially the snacks & goodies. They also have a Sanrio shop inside that carries a far selection of girl-ish bentos. We get many of our snacks here plus staples like rice & daigo (it's some sort of Guamanian pickled yellow radish thing, don't ask!).
Mei Hua Supermarket at Park and Coit - The other big Asian grocery store in Plano. They have a good selection of foods, but they don't typically have the boxes I have found at AWM. It's also further from my house, not that that should be a deciding factor for most people. ;o) I really like the in-store bakery, it gets many of its products fresh from a bakery off of Royal and they have some yummy sweet breads & cookies.
Shop Minoya at Parker & Independence - This is a really small little store kind of tucked into a strip plaza (it's near USAToy). They carry the snack items, but not as many basic groceries. However, they have the best bento supplies selection that I have found--cookie cutters, folding boxes, many of the kids' Hello Kitty & Shinkansen small supplies, foil cups, etc. They have really good prices as well, lots of stuff for under $2. It changes frequently, so we tend to pick up some of our snacks there so I can check out their new supplies. ;o)
I would assume there are probably some stores in Richardson and in Dallas (35 & Royal area), but we live in Frisco. Since I can get most of what I need in Plano, I haven't made the trek to either of those places yet to explore. It's on my to-do list, maybe once Faith starts school and I can drag Ben on these trips.