It's probably not the best thing I've ever done, but it's the best I can think of right now.
One time when I was on a camping trip while I was in Boy Scouts, this was probably when I was in 6th grade, I went to those outside bathroom things. One of the younger Boy Scouts came along with me, and before we went in I saw 16 dollars on the ground. I picked it up and asked several people that came out of the bathroom if it was theirs. No one was claiming the money so I decided to keep it. I also decided to give 6 dollars to the kid and keep the 10 dollars. Later that night an ice cream truck drove through the camping grounds and I bought one of those イチゴ ショートケーキ, ショート ケーキ popsicles. Those things are soooo gooooood.
There are many things I've done that I am happy I did. Such as the time I came out to my sister as an Aromantic Asexual. I was skeptical about it, so I made sure I could fully trust her. Come to find out that she's an LGBT supporter, so knowing this made it easier.
And once I finally came out to her, I was relieved to find out that she supports me 100%.
Fun fact: Hours after I came out to her, she came out to me as Bisexual. So neither one of us are Straight LOL