Everybody at some point will go through a period of struggle and it's what happens in those tough moments of struggle that define you, and those who've helped you. For somebody without any money, shelter or food, a small amount of cash can make a huge difference.
There are some people who are hestitant to give money to a homless stranger, fearing that their donation would be used to buy drugs. If you are one of those people, then worry not - why not buy them some food? Your small generosity will be recipricated one day.