Well, I would travel back to my 18 years old self and tell him to buy those damn ebay shares.
Back in the days a friend came to me saying "hey lets get some of those shares" and was like "no, it's not worth it, they never gonna make it".....damn I was so wrong, with the money I had back then, I would be filthy rich now xD
Well, there is another thing that I did, I hate myself for.
When I was 16 I met my first love. But cause of my personality disorder people kept telling me , that I am wrong and believed that crap.
But because of that, I kept my distance from her, to keep her save...Havent seen her since then and I am always wondering what could have been.
But I would never time travel to change the situation, cause I might have never met people I met because things went like they went. And also I know that she has a pretty good life without me. SO I am just happy for her and see no reason to take that away from her.