We have to think before we buy something. "Is this what I really want? And why? Is this what I really need?" If we buy everything you went, you can never save money. You have to think if it's really need to you. Or you shoud make a least before you go to the mall. And never buy someting doesn't write on the least.

We have to think before we buy something. "Is this what I really want? And why? Is this what I really need?"

If we buy everything we want, we can never save money.

Explanation: went is different from want. Went is the past tense of "go" while want is the feeling that you want to have something.
Explanation: You already began your sentence with we so you have to be consistent.

You have to think if that is really what you need. You should make a list before you go to the mall and never buy something that is not included on the list.

Explanation: You should not start a sentence with AND.
                   : A least means the smallest amount or number while a list means a record of information.