The most basic things you can do is speak up and boycott. If you are in a position to cut all business with Israel that is another avenue. I have friends in various startups and larger companies who have already ended contracts, stopped hiring in Israel, or blacklisted the countries IP.
But that's not enough, def con is coming up and many of us are going to strategize ways to completely dismantle them. "Never again" is not a saying it's words of action. Words and feeling sad is not enough, you must take action.