Fascinating insights from a Nokia researcher. Excerpt:

A couple of years back I carried out a multi-cultural research project with Per Persson and a number of other colleagues to figure out what objects people consider to be essential when they leave home. We spent time studying 17 urban dwellers in San Francisco, Berlin and Shanghai and Tokyo with shadowing, home-interviews, plus 129 street interviews and numerous observation sessions. One of our screening criteria for in-depth subjects was that people had to own a mobile phone although during the screening process we made no assumptions about whether they considered the phone a necessity or not.

In the cultures we studied 3 objects were considered essential across all participants, cultures and genders were keys, money and mobile phone. Whilst this may seem obvious the interesting part of the study was in understanding the reasons why people considered these objects essential (largely survival, safely & security), why they were not always present (forgetting, awareness, making a conscious decision to be out of touch) and strategies people adopted to help them remember to take these objects. A lot of times money will be carried in a wallet or purse, but when it comes down to it, the money (cash and notes) are considered the essential objects before the other objects that are also contained there.

Full paper reporting this research downloadable from here.