In light of recent events, the best thing to do (and the best way to send a powerful message) is this: Boycott opening weekend.
Don't attend NFL games; don't watch NFL games and let the sponsors of those broadcasts know what you are doing.
Don't be a sucker or a shill for the NFL and their wimpy copout on America.
Remember: The NBA requires players to stand during the national anthem. This isn't about free speech. The league can and does set its own rules. This is about common respect. It's about decency.
When the national anthem is played, you stand out of respect in the same way that any of us would stand for the national anthem of another nation if we were on that nation's shores.
Boycott the NFL until this rule is adopted and imposed just as it is in the NBA.