One of the things I'm doing is attempting to use cattle in a way that sequesters carbon in the soil in the form of humus. Others have had success using a combination of trampling and long-rotation grazing practices to boost soil carbon by many tons per acre, without requiring the use of machinery. Biochar is also a promising area for investigation, because you can combine that with heat and power production to get carbon-negative energy (using something like a top-lit updraft gasifier, or TLUD). If you then add a fast-growing coppice species as the feedstock, you have a sustainable energy production system that makes effectively permanent improvements to soil while soaking carbon out of the atmosphere at a pretty rapid pace.

On a smaller scale, you can change eating habits so that your food comes from sustainable sources (or even grow a lot of it yourself if you have space for something like an aquaponics setup). Learning to repair things rather than replace them is another small thing that has a large impact over time, keeping stuff out of landfills and reducing the impact of planned obsolescence.

If you want to have a larger impact than those things (which I understand may feel like insignificant posing), look to your local economic networks. Things like getting zoning laws changed to allow for integrated living and small business areas, with walkable streets, can have a huge impact on peoples habits in terms of driving and buying things from far away. That's getting into government territory, but it's local government so you have a much better chance of success.

If you're interested in tinkering, there are a bunch of things that can be done in the home energy arena that make a big difference. Start with improving efficiency (insulation, draft elimination, passive solar retrofits). After that, you can consider things like solar water heating, or high-efficiency wood heat for the dwelling itself. There are wood heater designs that you can build with minimal skill that are very close to as good as you can possibly get in terms of efficiency (look into rocket mass heaters or masonry heaters). If you make a job out of it, you can have a large impact over a few years doing these things for other people who want to do something meaningful but don't have the time/knowledge/resources to make it happen.

If you like biology/ecology, I think there is tremendous potential in the creation of passive productive ecosystems. The basic idea here is that we take space that is currently under-utilized (mowed medians, frontages, hillsides, unused lawns etc.) and plant them up with productive perennial species like fruit and nut trees, herbs, and various vine crops. Combined with minimal support from municipalities for allowing safe access, these kinds of areas can have a big impact on a lot of positive things - building connections in a community, providing a significant source of otherwise hard-to-get fresh fruit and nuts that's free for the taking, and at the same time providing habitat for wild animals to recolonize places we've been keeping functionally sterile at great expense. This is the other thing I'm doing on my property - creating a permanent productive forest environment (the cattle are part of the preparatory steps, and will gradually be phased out in favor of a tree-based ecosystem). It's easier to do than it sounds, if you just work on it a bit at a time. If you don't have land available, you can often find someone who does.

A business model I'm exploring in this space is the "urban farmer" or "urban forest farmer," who basically leases unused lawn spaces in cities and turns them into productive systems. The farmer would then harvest and sell the produce locally to make the profit - possible through a CSA arrangement. If you have the people skills, you can potentially get a large percentage of suburban or low-density urban properties involved for a given area, and you end up having "farm land" to use for local food systems and ecological remediation. It eliminates the need for mowing and other busy work for the owners, and they get a cut of the produce as a side benefit. It would also hopefully get neighbors talking to each other as they see the neighborhood transform, which combined with better zoning laws would probably lead to some local businesses springing up to support either your farming activities or things that follow from there (local restaurants, food preservation shop, etc).

There are a lot of options for improvement when you start looking at how things are being done today. Some of these things probably won't pan out, but others will, and the fact that we're starting now rather than waiting for somebody else means we're leading by example. Others will follow as they are able when they see what's possible.

I think the biggest thing is to change your mindset to think in terms of snowballing passive systems. Every time you make a wood heater for someone that uses half (or less) of the firewood to cleanly heat a space, you potentially save that quantity of energy every year after for the life of the home. Each productive tree you plant provides 500-2000 lbs of food every year for generations if it's maintained, and the maintenance is minimal. Half an acre of coppiced firewood species like Black Locust can provide the majority of the annual heating needs for a modest, well-insulated home forever. That's how you can maximize the impact of your labor - build things that keep on giving after you stop working on them.

There are loads of people out there right now who can't find a decent job. If we can make a viable business models for doing this kind of work, we'd have a huge force multiplier there as well by inspiring them to take on similar jobs, or even doing work that complements our own work.