I think the key is to
do the things you want to do but are afraid of doing.
Personally, I'm pretty sure I'm not going to regret not going on an around the world cruise, because I hate cruising, and have no interest whatsoever in doing it at all.
I will regret not getting my pilot's license, because it's something I wanted to do since I was like, 5 years old. So, I'm working towards doing it.
When we were children, we all had dreams of the things we could do when we grew up. As we get older, our dreams change, but all to often this change is a result not of us not wanting to do these things, but because we tell ourselves we can't do these things.
That's what we regret. Do those things.