What is the most important thing we can do for our fellowman? Is it financial, physical, or spiritual?

If they do not already know, tell them that their life is eternal even after the death of their physical body. How to make the most of it and to feed them especially if they have no food. Probably do this initially. Not continuously. Otherwise they will rely on you.

Most times people will learn how to work to feed/look after themselves and their families.

Matthew 22:39

The second, like it, is this: ‘You must love your neighbor as yourself.’

Galatians 5:14

For the entire Law has been fulfilled in one commandment, namely: “You must love your neighbor as yourself.”