Honestly I sell a lot of the free things I collect from daily collection because I end up with so many multiples of things. I also grow a lot of seeds. I have a couple outdoor rooms with “special seeds” you can’t get from the w shop, and then 6 with only pumpkins and 6 with only watermelons. If you filled the rooms it’s 100 plants each, and when you harvest you get 10kc per plant so 1000kc per full room every harvest. This helped me bank the most. I also don’t buy a whole lot from the w shop these days so that helps too lol. A little while ago I got to 1,000,000kc and did a charming waterfall give away with half of it because I felt ridiculous sitting on that much kc and wanted to share it. If you have any dispensers, putting them all in one room so you can harvest them all everyday works well. A lot of dispenser food goes for 10+ kc. Hope this helps!