The game tells you to collect shells and catch bugs and sell them, but this is not the most profitable option. You can sell bugs for 500-1000 dinks per bug, but shells are worth practically nothing.

Instead, you can harvest white wattle flowers and sell those. (Later in game you'll need them to make a brew but hear me out.)

The point is, any time you come across one the flowers you need to destroy them with an axe. This way, you'll get their seeds. And you'll find a lot of them exploring the map. They look like this:



Any time you find one of them, destroy them with an axe. Using the axe on them will also give you the 3 wattle flowers. Then, take your shovel, dig somewhere close to your base/tent, throw the seed (Q using the keyboard) and cover it with dirt/sand that you have on your shovel.

You need to wait for them to grow first, and that takes a bit of a long time. But after that, once they're fully grown, they'll keep producing flowers every 6 days which you can sell for a good amount of money. For example, I have 208 of them and I collect 624 flowers every couple of days, which I can sell for about 100k dinks.



Additional Tip: Bottle Brush Flowers are worth 100 dinks more than White Wattle flowers. You can find them on the dark green parts of your map. Harvesting their seed is the same as above. However, they are, at least in my opinion, much rarer than white wattle flowers. They look like this:



Still make sure to collect them whenever you see them, it won't be a huge profit if you don't have enough but every little thing adds up.

Once you have enough Permit Points, go buy the {Metal Detecting Licence from Fletch. This allows you to use a metal detector, which you can buy at John's for 6600 dinks.

Once you have the metal detector, use it with the left mouse button and start to walk. When you hear a different sound, you know you are near a treasure. You'll also see a blue circle on the ground. (Screenshots below) Check nearby with the detector and when it gives you a high pitch (also when the ground is marked with a blue sun) dig there. You can find materials lying around or barrels and crates which you need to break (any tool is fine.)





The types of materials you can get and their price: (The prices listed are with the commerce license level 1, which increases their value by %5, so you'll get 5% less if you don't have that license.)

- Old Toy - 1806 dinks
- Hot Cylinder - 3399 dinks
- Old Contraption - 16.599 dinks
- Old Gear - 577 dinks
- Old Spring - 2245 dinks
- Sliding Handle - 651 dinks
- Old Key ( do not sell these as you're gonna need them inside the deep mines)
- Old Wheel - 1452 dinks
- Shiny Disc (DO NOT sell these to John, instead give them to Franklyn, who'll give you about 8-9k per disc)
- Bright Wire - 699 dinks
- Glass Bulb - 1139 dinks
- Ear Hats - 919 dinks
- Green Board - 6732 dinks
- Smooth Slate - 819 dinks
- Button Board - 1712 dinks
- Tin Sheet - (crafting/smelting ingredient, wouldn't recommend selling these)

Note: All the items above are used for crafting and/or fixing tele towers. Please sell these at your own risk. Though you do get a lot of them usually, so selling half of them and keeping the other half might help.

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When you get Metal Detecting License 2, it says you're gonna be able to see the treasure spots, instead of using the metal detector. But, this is not always the case. In fact, you can still find most of the treasure spots using the detector. But every once in a while, you'll see the ground marked with an X. Like the screenshot below.

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Every once in a while when you dig for treasures you fill find a yellow-orange blob, you have to carry these to John's and drop them on his scale. He'll give you around 50-70k per chunk of amber but in my experience they are pretty rare, I've collected only one during my 45 hours of game play. But they're not used in anything so definitely sell them. (Note: You can't use any other tool/item while carrying the chunk of amber)

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When you cut hardwood trees with a copper axe (or an iron one, can't use basic axe though) sometimes a beehive will drop. (Screenshot below) You can break these hives using an axe or a pickaxe, and catch a queen bee to start your own beehive (which will give you honey regularly.) Or, you can carry them to John's just like chunk of amber. He'll give you something around 9-12k dinks depending on the weight of the hive.
Just make sure to plant some hardwood seeds near your home so you can have a steady supply.
Edit: Apparently beehives can drop from any tree, but I've never found any from other ones. Maybe the chance is higher for hardwood trees. (Thanks to Eric_showblade for correcting this!)

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In the Spring the Wary Mu nests spawn green eggs that you can pick up and sell in John's shop. Based on weight you can get around 8k - 25k dinks. If you check the trapping strategy below and use that as well you can make some significant bonus earnings from also trapping them. (Thanks to Tenoshii for this information!)

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You'll sometimes get a shiny stone when mining ore chunks, throw these at the stone grinder and they'll give you 3 random ores. But sometimes, although rarely, they will give you a blue gem called Opal and you can sell these for 15k dinks.

Also, again rarely, you can find Opal as an ore chunk on the map, it looks like this:

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By far the most profitable fish in game is the Barracuda, which can be caught with any fishing rod and fishing license in the Nothern Oceans during afternoon/night. John will give you 16k per one. (Thanks to [GER]KevTrev for this information!)

There are wish that John will give you more money for, but they're harder to find than Barracuda. At this point, the best thing you can do is to get a fishing book (you get it when you donate enough fish to the museum) which will allow you to see which fish is in the water, and how much is its value.

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For this you need the Trapping License and you'll need to craft a deliver zone and any kind of animal trap(s). You can lure animals into traps by chasing them into traps or luring the hostile ones, or just leave your traps laying around and hope they'll catch something (even the basic trap catches Roos and Magpies and they won't break out of it). Just take the crate with the animal and drop it onto the delivering zone, you'll receive your trap back and the dinks in the mail morning after.

Additional Tips for Catching Animals: (Thanks to "the Bishop of Blankets" for this tip!)
- Get the crocs to follow you and lead them back to the drop zone. Then when it's close enough wait for it to tire itself out or reduce its health bar and setup the trap directly on top of it. Then take the trap and drop it onto the delivering zone. Every croc is worth 9.6k dinks and you can do this multiple times with multiple traps.

Apart from everything else, you'll find rubies when you go into deep mines. They are like ore chunks but red. Break those rubies and carry them with you to the elevator, use the scale at John's and he'll give you around 50-100k per ruby chunk.
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A faster and profitable way to get rubies is riding your motorbike inside the deep mines, it can carry rubies, and since you can cover more ground at a higher speed with the motorbike you'll increase your chances of finding rubies. It also has unlimited light and the water is not deep enough in the mines for it to get destroyed. (Thanks Jaxevrok for this information!)

For a useful guide on deep mines, please check this thread