[paulcole]

Probably the only more impactful thing a person can do is not have biological kids (although admittedly the impact of an individual's veganism and child-free-ness is such a minuscule drop in the bucket that it's essentially pointless).

Since most people aren't willing to accept the importance of not having kids, it might make sense to donate money to people considering adoption or organizations trying to make it easier for people to adopt.