I'll usually just tell them no in a polite way. I don't like ignoring people unless I feel like my safety is being threatened by engaging with them. And sometimes they don't just want money, but any help. The day we settled the divorce case, a man approached me as I was walking back from the courthouse. I figured he probably wanted money but we ended up talking and while he was homeless, he was happy just being directed to resources. I walked him over to a drop-in center and he seemed grateful.
I should add that I don't feel as guilty saying no if I am spending time or money on organizations dedicated to helping people out. It seems like a "safer" way of helping people.