"Essential" is probably the right word, but I think "urgent" has a more accurate meaning. People urgently need groceries, being unable to buy groceries for a few weeks would be a big problem.

Some of the people who work in grocery stores commute via bike/car. Their bikes/cars will probably keep working for a while, but after a few months to a year they might need to visit a shop. The need for bike/car repair eventually becomes urgent.

Though, I'm not sure where hair salons fit into this framework. Most people have the means to cut their own hair, they just won't like how it looks.