Tom
Mental Arithmetic is a good example.
With the advent of calculators, mobile phones which have a calculator,
computers etc, IMHO the ability of people to do mental arithmetic "on the fly"
such as standing in front of a cash register has diminished.
Another one is Navigation. I was lucky and was taught how to Nav with
a Map, Compass and protractor, on land and sea. I see plenty of people in
a hobby I do who are totally lost if the GPS goes bang or runs out of batteries.