Four picks judged on what it takes to make them, not only on what they save once running. Each one uses very little material, and three of them turn something you currently throw away into something you use.
Vermicomposting (worm bin): A ventilated bin where worms eat kitchen scraps at room temperature. They turn the waste into rich compost, and a tap drains off a liquid plant feed called worm — Why this one: Turns kitchen waste into soil in a box under the sink. No garden, no smell, and the worms do the work.
DIY shade-sail window screen: A piece of shade cloth cut and hemmed to size, hung on hooks outside a window or glass door. It stops the sun before it reaches the glass, so the heat stays out — Why this one: The least material of anything here: a piece of fabric that stops the heat before it arrives, so no machine has to remove it.
Pedal / hand-crank generator: A small generator driven by pedalling or turning a handle. Your muscles turn it and it charges a battery or powers a small device. It gives very little power, b — Why this one: Human power, built from a bicycle you already own. Honest about its scale: it charges things, it does not run a house.
Urine-diverting dry toilet (UDDT): A dry toilet that separates urine at the front from solids at the back. Keeping the two apart cuts smells and moisture, and each is dealt with on its own. It us — Why this one: Separates urine from solids at the source, which is what makes the nutrients recoverable and the composting quick.
This is a short list, not the whole catalogue
All the solutions for your home are in the catalogue, organized by need.