I went to high school in inner city Cleveland and worked downtown (and walked about a dozen blocks from the bus or parking lot every day). Have had much exposure to homeless people. Here are some thoughts:
I don't know if they still have them, but an old practice among the generous was to carry McDonald's gift certificates with you, so when someone asks you for money, you can offer them that.
Why? Because the majority are using it for booze/drugs/wine/drugs/etc.
I remember I'd often offer a portion of my brown bag lunch to people who said they were hungry, and they weren't interested.
If you picked up a homeless guy and he was actually hungry -- cool. But he's probably literally one out of fifty who wasn't just trying to collect drug money.
In Cleveland (and most U.S. cities), there are numerous homeless shelters and soup kitchens, etc. These places are run by dedicated volunteers, they are very efficient with little money and are able to feed more people per dollar. Every homeless person knows where they are; if you ever feel the need to be generous, that's a good place to donate money.
As for the dangers of picking up a stranger . . . I have more faith in the goodness of humanity than some of the more jaded/insulated types. I think God will look out for you when you are genuinely doing something to help another. You hear all kinds of stories about people who got kidnapped/slaughtered/mugged/etc. when helping a stranger, but a) the majority of those "stories" are told by people who turn their noses up at the homeless and have never been near them (much less stopped to help someone), and b) for every one true negative occurrence we hear about, there are many, many acts of kindness and generosity like yours that go unmentioned, unrecorded, unknown by others.
Sure, you have to have some street smarts, but unbeknown to many of the people hiding out in their suburban cul-de-sacs who think the city is a terrible and dangerous place, there are as many good, honest people in the ghettos and slums as there are anywhere else, and these people deserve the same respect as someone golfing at a country club or shopping at a pricey mall.