It doesn't matter if someone uses resources responsibly if someone else comes along and then uses up what's left. People defer power to higher levels - government, companies, religion, culture, education, etc. Real change involves people but will have to be driven by one of these if you want entire populations of people to go along.
Climate change is unfortunate since it means getting many countries working together, and some may see a benefit in doing nothing.
As to what people can do? I'm not sure there is an answer. A technological solution would be great but isn't assured, voting is a problem in that you already need a lot of people thinking the same way, and leading a good lifestyle will assuage personal guilt but move the needle very little, so I think it's worthwhile but not a solution. I am not sure it will make a difference as you say when others will step in and consume what you left on the table.
My opinion is that nothing meaningful will happen until we see some obvious signs of distress and even then we'll be lucky if people scramble for a solution. We are starting to see problematic weather patterns, reef bleaching, and other evidence but since the problem is statistical in nature we always get people who say such events are not necessarily an indicator of a problem. Broader scientific literacy in the community to understand the fundamentals involved would take a generation and would have to be led from the top down meaning we get back to the same issue of bringing an entire country on board.
So I don't have an answer, but I don't think someone always needs an answer to point out something isn't working. Regulation would work within a country, but you need to get leadership on board and this is a global problem meaning one country isn't enough. The solution will have to align with selfish interests whether economic or actual survival. My hopes are on cheap green energy and maybe one of the cleaner variants of nuclear but that is more of a faith-based answer than anything. I hope it'll work out but don't know enough to be sure.