I don't really have any regrets, or rather, I don't have anything I still regret. I might regret something for a while after it happens, but that fades with time.
I'm happy, I like my life, any decision I might have made differently in the past, even if the direct result of it was better, might have made my life worse in the long run.
For instance, I mined about 10 bitcoin when it first became a thing. And then I just... forgot about them. They were a silly little thing that were worth a couple of quid, so they sat in a file somewhere and then when my harddisk died I didn't even think about them. Until a few years ago when I found out just how much a bitcoin is worth these days. I could have been a millionaire!
So yeah, it'd be very easy to regret that. But if I'd had that million quid, then who's to say my life would be the same now. Maybe having that extra money would have meant that we'd buy a house, that we'd end up unhappy in, maybe DD would have been bullied at the private school we'd have hypothetically sent her to. Maybe me having extra money would have revealed my brother to be grabby cheeky fucker. Any one of a million different pressures on my life could have made it measurably worse than it is now.
I'm happy, now. Why would I regret anything that got me to this place?