planting a bunch of non-native trees, and tting every 3 days to get fruit and sell it. I make like 185k from my fruit island for my main island. Other than that, turnips.
Make a foreign fruit orchard and sell them every 3 days. And invest in the turnip stock. Buy low, sell high, I sold 4k turnips monday and made 2.5 mil.
Everyday sell the seashells that spawn on the beach. Catch the most expensive butterflies you see pop up (there’s lists online that tell you how much the insects go for) ((I suggest also reading into making your own tarantula island where you can rack up a lot of money with tarantulas and atlas moths)). Create an orchard with non native fruits so you can sell them every three days. Fish. With that in mind, collect lots of manila clams that you can find in the shores sand, create fish food, go on your dock and continue to scatter the food and collect lots of fish in a short time spand.
Turnips is the fastest way in general if you timetravel. Sometimes when I see someone here post about really good turnip prices, I TT to my last sunday, buy a full inventory of turnips and go straight away to sell them. I've done that 5-6 times and I earned around 12 million just from that. You can also sell items you don't need or sell cataloging here on this site. But other than that I catch the expensive butterflies, collect and sell seashells and unused fossils, I've made an orchard with non-native fruit that I sell from every 3 days, I also fish and go to nook islands and grab everything I can collect or sell.
I don't time travel, but I saw this idea that seemed very easy. Deposit 100,000 bells (I think that was the amount) into your ABD account. Time travel 10 years into the future and you will have a letter notifying you that you have 99,000 bells in interest. Time travel another 10 years, another 99,000 bells. I think they said you can TT to 2060. Just takes a few minutes. You can do it with a smaller deposit, but you won't get 99,000 bells, at least the first time. You will have bed head and some weeds on your island. When you return to current time, you will still have all those bells.
Turnips are the easiest and fastest way to turn bells (up to 2,000,000 a week if you have an inventory full if you do it correctly). Buy low and sell high (buy at like 90-95 per turnip and sell at 400-600 per turnip) and you'll get a really good profit every week.
Otherwise I like to fish between 8pm and 10pm and I tend to make about 100k an hour that way.
Question: What's the fastest way to get (insert item here)?
Answer: Time travel
If you don't want to TT, it's best to do a combination of things to make bells. Hitting the money rock every day and planting 10k in the glowing hole are a good way to make a consistent 37k each day. Planting a foreign fruit orchard gives you another quick and reliable income source. Having a large field of flowers including hybrids to attract valuable bugs provides another income stream. Check the hot item at Nook's each day because it can be worth a good amount and you can craft a lot of them to sell. Finally, going to mystery islands and clearing them out to increase the spawn rate of tarantulas can get you a lot of bells quickly.
Stalk market is the #1 way to makes bells, but you either have to play every morning and afternoon to check prices, or go to someone else's town to sell. They require you to have a lot of bells of to make the investment and they are higher risk than the other strategies for making bells.