Zojirushi’s Mr. Bento Lunch Jar is a modern spin on the Japanese bento box. However, it will keep cold things cold and hot things hot. Mr. Bento features four microwaveable containers: a watertight soup container, a large main-meal container with an insulated lid, a smaller container I use for salads, and an even smaller container for snacks like cheese/grapes. All these containers stack neatly inside a stainless jar in a specified order that creates a seal, keeping the soup/main container hot or cold while the other containers remain at room temperature.
Mr. Bento also comes with a spork, so you don’t have to carry extra utensils; the spork even has a cover. Mr. Bento himself fits inside a nice bag (included) that has pockets for napkins and the like, and enough extra room for another small food container should you desire a bigger meal. In my case, I typically take a small container of oatmeal to work, so I just place Mr. Bento on top and put the entire stack in the bag. A fully-packed Mr. Bento with bag and utensil weighs around 3 lbs.
As for how long things stay hot: Typically, I pack my lunch around 6:45 a.m., then don’t eat until 12 noon. I never feel the need to microwave. For example, recently at 7 a.m., I microwaved a frozen burrito and cut it in half to fit in the meal container. At 11 a.m., the burrito was still hot and steam came from the container when I opened it. Zojirushi advises preheating the jar with hot or cold water for maximum temperature retention, though I’ve never tried that.
When you first look at Mr. Bento, you might worry you’re going to walk away hungry. Your mileage may vary, but I am a whopping 240 pounds of man and sometimes I wonder if I should have purchased a smaller Bento like the Ms. and mini (I also have Zojirushi’s rice cooker).
My impetus for buying a lunch box was that I discovered I was spending over $100/month going out to lunch. I wanted to save money and did not want to get bored eating-in. So far so good! I also found Mr. Bento has a cult following, including the “Mr. Bento Porn” group at Flickr (Despite the name, it’s safe to look at during work). This is what really sold me on it.