Buy them food, donate clothes, volunteer at homeless shelters, etc.. most importantly, treat them like a human being..

I did my nursing mental health placement with the homeless community in Australia. Many of them are looked down upon by people, called junkies, and what not but people don't know their story. So many of them grew up in dysfunctional homes where abuse(physical, sexual..) are so common, neglect is also very common where their parents do drugs in front of them, they get no love and support like how a normal child would which is why they resort to drugs to numb their pain. Drugs are not the problem but the symptom of the problem.

I remember during my placement, we had this man who is 6'5", massive guy. He is a drug user, has schziopernia, was abused as a child and has a lower IQ than average. Because of this, he is very easily influenced and taken advantage of by evil people. I remember when the social worker approved a unit for him to live & got a support worker to come by weekly to spend time with him, he just burst out crying of joy.