During big earthquakes, these elevators stop working. An earthquake in 1992 resulted in most elevators in Tokyo stopping; many didn't restart for an entire day. Another earthquake in 2005 left 64,000 elevators paralysed, according to Cameron Allan McKean of Next City, and some people were stuck up in elevators for almost nine hours after a quake in 2011.
In response to these incidents, Tokyo created the Japan Elevator Association Kanto Branch (JEA), a body that conducted research that showed thousands of people could be stuck if an earthquake struck (the current figure stands around 17,000). The association devised a number of methods to try to avoid this, including backup power sources and early warning systems that help people escape elevators if an earthquake strikes.
These technical solutions will never work all of the time, however, and it remains likely that people will end up trapped in elevators if a large earthquake comes.
Toilets, drinking water and other amenities would no doubt make those people far more comfortable until they are rescued. In fact, some local governments have begun putting portable toilets in elevators.
According to Jiji Press, Tokyo's Chiyoda ward began putting in "water, blankets and emergency boxes that double as toilets" in 2014, with other parts of Tokyo planning to follow this tactic.