That was very nice of you MK, as stated acts like that can do a lot more than just the act of giving someone money.. Whether or not this person goes back and throws it all back into a gambling machine, is irrelevant. I've done something similarish.. - Back when I was living in London, I did my shopping @ the same local grocerystore most times. There was this dude I had come to talk to, who used to stand outside with his guitar playing. He was one of those type of people that get everything thrown at them in life, and I honestly felt sorry for him. His partner also had a young baby girl. Frequently gave him any spare change that I could afford. Anyway one day I had randomly bought a £2 ScratchCard/Ticket, and won £500. I proceeded to fill up a basket with everything you would need for about 2 weeks for a small family, ended up with like 3 shopping bags full of food/household things/nappies & baby wipes etc ( spent about £50 ) and then walked out the shop and dumped the bags next to him. Guy burst into tears, he was sooooo appreciative. Shame. Haven't seen him in years now. Wonder how he's doing..
But yeah, those random acts of kindness ( no matter how small or trivial they may seem to us ) can do a lot more than just that single act of helping someone. It may help trigger change in them - to try get aspects of their life heading in a more positive direction, get some positive thoughts coming their way that may help them out of the shitty life situation that soooo many people find themselves in during those dark moments of life.
Anyway, thats my 2c worth. In essence, if you can afford it, and it gives that unfortunate person that meal they so desperately need, then do it. Karma doesn't forget acts like this.