Small things that aren't in direct contact with people, and much of which probably benefits animals more than humans, but they matter too, so...
I often pick up trash people leave where they shouldn't, and bin it. I can't stand disrespect for the general area in the form of garbage left around when there are bins.
I periodically cut back brambles and branches growing across a little foot-track through woods, which is used as a short-cut in the local area. Nobody, not even the forest keepers, bothers much with this little woods area, but some of us do things to maintain it. We don't even know each other but I've run into another person trying to keep it nice too.
I closely monitor the resident colonies of waterfowl on my local lakes in parks, and keep an eye on their welfare. I know quite a few of the birds on sight individually and up close, and I know if they are missing, injured etc. I recently removed a plastic bag from around the neck of a swan who already knows me and let me do this. I report violations of forest regulations. I got a local news source to report on an issue, creating greater awareness on a problem.
I'd like to start doing some "guerilla gardening," which is when you plant beautiful things in public areas that aren't cared for, in some neglected tree pits near me, but apparently there's a huge problem with people stealing the flowering plants you seeded.