First of all, adventure is to find treasure, which is why most pirates go to sea. It is precisely because of Roger's news about the big secret treasure that countless people have gone to sea to look for it, so the treasure is fatal to most people. I believe that Luffy's original purpose in going to sea may also be to find Roger's treasure. Although the straw hat pirates have not found Roger's treasure so far, they have found many other treasures.
The straw hat pirates have experienced so many adventures, such as harvesting a lot of gold on an empty island, which is commendable. In addition to the empty island, the Straw Hat Pirates should have gained a lot of treasures in other adventures. Coupled with the straw hat pirates along the way, they defeated many powerful pirates. These pirates must have a lot of savings, but they were not all cheap in the end.
The life of the straw hat pirates is not for three years, but for three years. After defeating the powerful pirate group, it must be a lot of money. After all, the Straw Hat Pirates have financial fans like Nami, and it is almost impossible to miss the enemy's treasure with Nami.
The second income of the straw hat pirates group should be donated by others along the way. The Straw Hat Pirates Group is a kind pirate group. They have helped solve some local problems along the way and will naturally receive many gifts. The Meryl that Miss Kaya gave to the straw hat pirates is the most typical example.
Besides Merry, the straw hat pirates also received many gifts. Luffy's greatest advantage is that he can become good friends with all the people he has interacted with. Since the long voyage, the straw hat pirates have established diplomatic relations with many countries, such as the desert kingdom of Alabastan, Mermaid Island, Daughter Country, Dresden and so on. And they can all be counted as loyal allies of Luffy. Luffy also helped them a lot, so when Luffy went out to sea, it was estimated that they all sponsored Luffy a large sum of money, so Luffy would not be short of money at all.
Finally, there are not many places where the straw hat pirates spend money. Straw hat pirates spend most of their time sailing at sea. They just need to ensure some basic living expenses. Big aviation is also rich in products, and Luffy can often be seen fishing in the plot.
So many places where they spend money can even be self-sufficient, and a small amount of money is enough for them to use for a long time, so the straw hat pirates basically don't need to worry about money.