Area of greatest demand, financially speaking, is probably holidays, with all their associated insurance plans. Travel is a great form of education, though, and I will always wish to be able to do more, so perhaps my greatest demand is for more time.
As a teacher of English in Thailand, my area of greatest supply is in demonstrating the ways that meaning can be conveyed verbally.
Some of the supply that I generate is therefore matching my own demand 🙂 because I’m always learning something new.