My father once gave a guy a bill (currency) that surprised me and I asked if the drugs / alcohol possibility bothered him. He told me that if the guy humbles himself so much as to ask then he clearly needs it and that if he needs a bottle to get through the night then who was my dad to judge. It had a pretty profound effect on me.
Don’t beat yourself up if you can’t afford to donate. I’ve gone dumpster diving for food and picked fruit from trees and bushes under cover of night. I couldn’t donate a penny in those times because I was counting cents to buy small bits of food. Sometimes you just can’t take on more responsibility.
Now that I have a lot of comfort, I try to give as much as I reasonably think I can because I believe that if I’m able then I should. For instance, I will never turn down a request to buy someone a meal and I hand out cash in larger denominations than I think people expect depending on the circumstances I observe. But I still don’t give money to just anyone. If someone seems sleazy or like they’re trying to con me (it’s subjective), I’ll decline. And again, I don’t feel bad about it when intuition tells me that I should decline because I genuinely want good things for people and I know that about myself; in other words, I trust myself not to be a dick.
One other item: I once bought a woman a sandwich even though she kinda had an entitlement attitude. I got asked for money by a guy a block up the street and declined. He was rude to me as a result. I yelled fuck you at him because what he said to me deserved it. He had no way of knowing that I’d just given $20 to a stranger, but that didn’t make it acceptable for him to say what he said and I feel no regret about giving him a piece of my mind in response.
That you’re thinking about enough to ask strangers on the internet suggests that you have a good moral compass. Just try to pass along some help to others when you’re better situated in the future. It’ll be fine.