It depends. If I'm in a rush, no. If I'm short for cash, no. If I have no small change, no.
But if I'm not in a hurry and do have small change, often I do give people something.
I'm a utilitarian, and I believe that everybody else's happiness is as important as my own. Anything else would be treating humans unequally, when we're all equal. I don't always manage to live out my beliefs, but I do try. When it comes to a person on the street asking for my money...
First of all, what am I going to do with that money? Normally I come across homeless people when I'm travelling places or out shopping. Small change for me goes on hot drinks and snacks. These are unhealthy. I shouldn't be eating/drinking them, and they are also indulgent... I can meet my own nutritional needs better and more cheaply by packing healthy food. So really... if a homeless person uses my money on alcohol or drugs, I don't think they're wasting it any more than I would be wasting it irresponsibly myself. Why should I hold them up to a higher standard than myself? And why should my instincts to indulge be more important than theirs'? I am a chocolate addict. Addiction to chocolate, or other bad habits of mine like never sleeping... carry much less social stigma than drugs or alcohol do. But if you look at these things honestly, in moral terms they are identical. I am no better than a drug or alcohol addict.
The second reason is that if you are living on the streets and begging, your life has got to suck. Nobody does that if they have the option of a normal life instead. Every day somebody lives like that, they will have people looking at them, judging them, and making them feel like dirt. Yes I'm sure that some exaggerate or lie about their condition in order to get donations, but that doesn't mean that their lives don't also majorly suck. By giving some money, I might help make their life suck a little less. But also it's about being kind and communicating the fact that I recognise that they are people, and that they have worth. Sometimes kindness and acknowledgement are the most important thing you can do for a person... more than the actual money you're giving.
It really makes me sad how the Daily Fail and right wing government have nudged Brits into this miserly attitude, and obsession over whether people 'deserve' benefits or whether they're 'taking responsibility'. Poverty, addiction, homelessness...these are complicated problems that involve a lot more than individuals and their choices. Few humans have meaningful choice anyway. All of us are who we are because we had certain opportunities to choose between. Every human makes choices they regret and does things in their life that are unwise, and have bad consequences. And there are more than enough 'real' homeless people who are truly desperate. Why punish the whole class for the one kid's misbehaviour?
At the end of the day, most of us aren't really going to miss the occasional £2 here and there. So why not use it on making another person less miserable? Or is that latte you were going to drink really going to transform your day in the same way?