I decided to add legal and ethical to the question in case somebody thinks doing something illegal or unethical would make the world a better place. It doesn’t have to be big or world changing. It can be something as simple and easy as giving a listening ear to somebody. I saw an example of this a while back. A person was wanting money from somebody who didn’t carry cash. The individual did listen to the other person for 15+ minutes as it appeared the person needed someone to listen. I wasn’t close enough to hear the details, but from what I could see, the person was not used to be giving the time of day, much less having a complete stranger listen.
There are plenty of ways to help that don’t cost a lot of money. I was with a friend who volunteered once a month for a few hours on a local warm line, https://www.madinamerica.com/2014/06/warm-line-expect-call-one/.
A warm line is an alternative to a crisis line that is run by “peers,” generally those who have had their own experiences of trauma that they are willing to speak of and acknowledge. Unlike a crisis line, a warm line operator is unlikely to call the police or have someone locked up if they talk about suicidal or self-harming thoughts or behaviors. Most warm line operators have been through extreme challenges themselves and are there primarily to listen. A warm line has the purpose of reducing hospitalization and forced treatment, being a cost effective and non-intrusive, voluntary intervention.
I volunteer a couple of times a week at a local historical/genealogical society. The society has no paid staff. Everybody is a volunteer.