Egg molds - I used a small egg, molded it while hot, and left it overnight in the refrigerator...no difficulties with shape retention.
Bento boxes - we have one of those classic Zojurushi bento pails, Chris, and it is a bit heavy. I have used it mostly to leave a complete dinner on the table when one kid needs to come home, eat, and go out again in a hurry while I'm out! Son1 occasionally took it when he didn't have much else to carry, or far to walk.
Our standard winter bento is like #4 or #8 in Prasantrin's link...an insulated container for rice, with two separate containers for side dishes. There are many variations of this type - they are lighter than the pail type, and the hot rice makes more of a difference than whether or not the side dishes are hot or cold. In fact, it is more useful to be able to pack fruit etc. when you DON'T want it kept hot!
During warmer weather, we use #22 in Prasantrin's link...some reviewers complain that the side-containers are too small in relation to the rice container, but I often layer the rice with something like egg soboro, salted salmon roe, or Okinawan andansu miso-pork. That container has an aluminum rice container (cools faster than plastic in summer, when rice spoils easily), with two separate lidded plastic containers.
One good thing about this type of bento box is that the containers tend to be a little deeper than the old-style bento boxes - making them more versatile. A shallower top layer (like those below) is a little harder to pack large items in, though it makes it easy to arrange bento foods attractively and helps to KEEP THEM FROM MOVING ROUND.This
Shokado-style bento is also a family favorite...we use an older model, but it's much the same: plastic deep bottom layer has a removable divider, allowing you to pack less rice if you prefer. A press-down mold (wet first) allows you to mark bite-sized divisions in the rice, not only pretty, but easier to eat during short lunch breaks. The top layer in our model at least is sometimes a bit shallow, but the removable H-shaped divider is very handy - you can have 4 divisions much the same, or none, or slide it along so that you have one large, 2 medium, and 1 small division. If you scroll down the link page, you can see another variation with an avocado-green lid. These two are a bit smaller, better for women or "normal" adults...the one with the black lid (swirly design on top) is the one we have, and it's just a bit bigger. Too big for my husband, fine for teenage boys.
Some of my son's friends like this type of donburi
bento - rice with topping, for the kid in a hurry - just open wide and inhale! Those with particularly large appetites for for a Tupperware lidded salad bowl...Flat bento with insert containers
this type of box is out of fashion, but is what my husband takes each day. He likes the fact that the rice container isn't too big in proportion to the side dish containers, and the two containers keep items in place and separated...no sneaky movement of sloppy ketchup from the meat to the omelet! Snag - all these bentos with clip-on lids will eventually need to have the silicon rubber packing replaced - we keep a small supply (in the appropriate size) of Slim bento
boxes are popular with women - too narrow for sandwiches, but the smaller ones are enough for a woman, and narrow enough to fit into a big purse easily. I had a particularly skinny one that I found very easy to pack (just line different items up in a row!) and easy to eat from.Round
bento boxes with a soup bowl for a lid are also especially popular with women. You can't carry soup in them, but they are handy if you like to make instant soup at your workplace.