Lockers. Yes, lockers. Or more specifically, the coin-operated lockers you can find at pretty much any station, shopping area, department store, stadium--you name it--in Japan.
Living in this country as long as I have, you come to take it for granted that there will be a safe place to store your junk while you go about your business. Whenever I travel to Tōkyō, for instance, one of the very first things I do after arriving is go to Shinagawa and dump my carry-on bag into one of the hundreds of lockers they have in the station. Many of these can be operated with IC cards (Things I love about Japan #6) so you never have to worry about having the right amount change. (Many also have automatic cash changers nearby.)
Now, try doing this in the States.
A few years back, I did in San Francisco.
When I tried a search for "coin lockers" on GoogleMap, a couple of hits came up. So, I headed off in the direction of one arrow after another, but none of the places which claimed to have coin lockers did. After several disappointments, I resorted to asking people on the street if they knew were I might find a locker. A coin locker in the city? You would have thought I was a homeless man with Tourette syndrome spouting off nonsense the way they looked at me. In the end, I had to agree with my wife that it would be better to just schlep the bag as we went about our sightseeing. (Problem is, we had our boy with us at the time.)
I might as well add Things I Love about Japan #7 to this here. It's related to Things I Love about Japan #3; namely, you can trust the Japanese to not only leave your stuff alone when you go take a leak, but you can rest assured that when you stow your things away in a coin locker, overhead cabinet, or in the care of a cloakroom assistant, 99 times out of 100 nobody is going to try to dick with it. I know it must sound like a radical idea that people can be trusted to keep their hands off of your property, but here in Japan, Buddhists and atheists are much better at obeying the Tenth Commandment than the good Christians back in America are.