Hard question to address.
While I’m a hippy too, and agree with the flower-child love-everybody life goal, I have found that love, unfortunately, is not always enough.
Perhaps the easiest part of your question to respond to is the “fewest regrets”. Simply speaking, the answer would seem to be not to do anything regrettable. How do you determine what might prove regrettable? For me, that is basically showing consideration for others in all that I do and letting others live their own lives with as little interference from me as I can manage. Live and let live, so to speak.
Rich and meaningful, Hmmmm. Meaningful is a subjective term. What is important is what is meaningful to YOU. Do you want to achieve world peace? End tyranny in a third-world country? “Save the Citizen?” (see the movie, Sky High). Help foster children grow up to be responsible members of their community rather than hoodlums or criminals? Meaningful is a personal thing. It is based, in part, on your own spiritual/religious beliefs or lack thereof. It is based on the accumulation of your own life experiences. Of course, if you are 18yo and just starting your adult years and don’t want to spend a couple decades trying to figure out what to do with you life, well…
What do you enjoy doing? What do you enjoy reading? Or viewing? Do you love animals? Maybe rescuing or supporting rescue efforts is what you want. Do you imagine yourself as a doctor, a fireman, a lawyer? Maybe become a candy-stripper in a hospital, a hospice assistant, a trainer of Dalmatians for fire stations, a lobbyist, a paralegal. Are you a sports enthusiast, into sky diving, cross country skiing, professional ice skating? All sports events need volunteers to support the participants, prepare the turfs and clean up afterwards, provide first aid and sometimes just support staggering athletes.
I think the life activities that are most likely to make your life, in your own view, rich and meaningful, is to take something you know about and/or enjoy and support it, not only monetarily, but through non-paying, non-rewarded personal involvement. Help publicize it by sharing it with others, through publicity, and through your own participation. Contribute to it, yes, if you can, but get personally involved without expectation of recompense or reward, or even a thank you.
For me, meaningful is believing the example of my own behaviors somehow improved or enriched someone else’s life. This is what makes me feel my life is rich, or in my own opinion, worthwhile. And the only reward I look forward to is the approval and appreciation of My Creator, when S/He welcomes me back to His/Her loving arms one day.