Mentor kids other than yours
Even if you are NOT a father, you'll never know how much influence you have over kids. They watch our every move. When I was growing up (after my dad had died early) I found 5 or 6 neighborhood men and hung out with them constantly. Each one had something that made me pay attention and model what I saw.
Just asking a neighbor's kid how things are going on the team or at school is huge for that child. It makes him feel special. If you have time to do more, of course, that is great. It's the best investment in the future you can make!