If I find money in my car and don’t know who the owner is can i keep it? Can I give it to tzedaka?
What about an object? If i find money at a gas station can I keep it?
Whereever you find money, it is permitted to keep it for yourself. If there is a reasonable way of finding the owner (you know who sat in your car), it is worthy practice, though not oblibgatory, to return the money to its owner.
For an object, the halachos are more complicated. If there is a siman, a clear mark of identification, on the object, you have to make an attempt to return the object to its owner, by means of the mark. Even if there is no way of identifying the object, there remains an obligation, in many cases, to return the object. Where this is not possible, the value of the object should can be recorded for the future (this is the amount you’ll have to pay the owner, if the owner should one day be found), and the object can be kept for yourself.
These are the halachos in a nutshell, but their full scope includes many more details.