Leaf Mould: An essential ingredient in many DIY organic fertilisers. https://youtube.com/shorts/K3570wISvJo?si=hc_dlXGGQkNb4Qyp
Making a liquid Calcium Acetate soil amendment, using egg shells and apple cider vinegar. This is a chemical process, not a biological fermentation process...for plants, not for human consumption.
Milk that's getting a little nasty can be used (watered down) to add calcium to the soil, for your tomatoes. Crushed chewable Tums (generic are cheaper, of course! LOL) can be added to a watering can, to add both calcium and magnesium. Compost "tea" is always a good choice, for any crop. EDIT: I have removed the info about putting banana peels in a pitcher of water, for a potassium boost. I recently saw where this method is not advisable, due to the fact that you can end up fermenting the bananas if they spend too long in the water. Which is NOT what you want to water your plants with!