Solarpunk

So I have two:

Land conservation is huge - especially the creation/preservation of greenways, corridors that animals follow because there are fewer human encroachments there (whether new neighborhoods replacing habitats, or roads which present a threat to any animal with a need to roam). Conservation is a huge task to take on solo -- you're looking at all the expense of purchasing land, without much or any plan to profit off it, so basically nobody in our society really understands it, (most people will look at you like you're crazy, and banks aren't likely to help without a plan to develop). I've tried and failed at solo conservation. But there are other options - land conservation nonprofits can make it possible - I've worked with, and volunteered with one and they're amazing. So I guess my addition for 'simple' is find one you like and consider donating or volunteering. If you already own land, consider easements which could prevent further development or extraction of resources like mining - conservation nonprofits will cheerfully help you get this done, and will probably fundraise for it, including paying you the value 'lost' by adding restrictions to your property.

My other one is simpler - join a Buy Nothing group and change how you think about, acquire, and dispose of stuff. When I moved to my current town, I found and fell in love with the concept of "Buy Nothing"/ "Everything is Free" groups (I've written a longer post about them here https://slrpnk.net/post/354527). The short version is they're online groups, usually covering a very small geography like a town, where people can either offer up things they don’t want anymore rather than throwing them away, and where people who need things can post a request or In Search Of (ISO) for specific things in case anyone has one they don’t need. They're awesome because they're a way to meet and help your neighbors, and keep stuff out of the landfill. They're punk because they completely challenge the capitalist, individualist structure of our society in small, day-to-day ways. Our 'ideal' capitalist society has us all siloed, isolated from our neighbors and churning through products as fast as possible. Places are destroyed and resources are extracted so they can be turned into products, sold to consumers, used, and then thrown away. Maybe they're broken at that point (could they be fixed?) but it's just as likely that they're just old, unfashionable, or the person throwing it out doesn't have room or a need for it anymore. We're not supposed to know or care if someone has the exact thing we need sitting dusty in a closet or if we're throwing out something someone in our town is on their way to buy, because that would slow the whole cycle down and generate less money. Break that cycle, buy fewer new things, fix stuff, give it away for free.

Other people have posted longer lists with a broader range of examples, so I feel okay sticking to the two I'm pretty evangelical about. Good luck!!