For example, how much value do you put into close relationships versus distant ones? Is charity worthwhile if it helps someone who can't help you back? Maybe someone who doesn't even know you?
edit: reworded.
Having beliefs is not the same as having religion.
Even having theistic beliefs isn't the same as having religion.
Btw, even taking a very atheistic perspective, only focused on how humanity evolved (which is a selfish process in spite of your future protestations of how you have trascended it) we can see we evolved to be nice only out of self-preservation.
One would think that is the ultimate personal gain but I'll grant you that reminding yourself you are a good person must be a psychological gain of its own.