Beautiful thread.
One of the nicest things that happened to me was when I had a miscarriage the lovely nurse that I saw afterwards just gave me a hug. It was unexpected - the human contact - and I really needed it. Then when I got pregnant again I went in for a scan and some blood results - I can still remember her doing a fistpump and shouting 'YES!' when my bloods came back fine - she really cared.
More recently, I broke down on a baking hot day this summer with a young child in the car, and a man who owned the café across from where I broke down brought two bottles of ice cold water and some biccies across for us as we waited for the RAC.
My first one I did was when I was really young - we were going on a rare holiday (just a train up to Scotland as we didn't have much money) and we passed a young boy about my age (14ish) sitting on the steps in the station. I walked with mum and my brothers into the station but felt horrible all the way. Then I suddenly made up my mind and told my mum I'd catch up with her, and ran back up about a zillion steps to the boy, and dumped my precious £4 holiday savings into his hand. He looked stunned and I had to rush off to catch my train (and catch up with my very anxious mother).
I also later looked after a homeless guy in what turned into a bit of an epic saga - started by buying him a sarnie and drink in Greggs and then asked him if he'd be ok for the night and where the nearest shelter was. Walked with him to the shelter but he couldn't get in and so we walked to another one they directed us to, stopping to buy him a bit more food on the way. He was absolutely barking mad and told me his life story as we walked around, including how he was the secret love child of Goldie Hawn.
My most recent one was actually today, when I was in a shop and a woman was taking her visibly anxious and profoundly disabled teenage son around the shop in a chair. She kept talking to him, staying so calm and soothingly telling him 'You're doing so well!' whilst he kept seeming to panic and shouting 'Mum' and making distressed noises and hurting himself. Eventually when she'd parked him temporarily and come over to get something off a shelf near me I said, 'I think you're doing so well too!' with a smile and her face lit up and she said, 'I'm having a rough day actually!' and I said 'Well I think you're a fantastic mum, so patient and amazing' and she cried (and hurried off grinning). I think sometimes it helps to have someone recognise that you're having a hard time.
I always try to do little things, too, like give parking tickets, help older people with their shopping etc.