I was just talking about this to my husband the other day.
Of course there are things that I would like so much not to have done... curiously enough, the two I remember are related to scolding young kids, because I don't believe today that scolding kids does any good to them.
One of those kids was one of my younger brothers. I remember years ago apologizing to him about it... he was laughing so much... he was unable to remember. Of course, my scolding was probably one in the zillion he used to receive, from our parents, teachers, etc. ... he was our local version of Dennys The Menace :-)
Those let aside, what I am really sorry for are not "things", but rather "not things", i.e., the things I didn't do. Mostly not to have been present enough, loving enough... to my parents, grandparents, siblings, friends, neighbors. Even today, I would like so much to be more present, more loving... but such is life, one gets absorbed in our own interests, own problems... Little by little though, I try to get closer to my ideals.