Voting matters. I'm in a deep red state and will vote blue. There's zero chance the people I vote for will be elected.
My vote still matters. It still influence the flow of money both locally and nationally. It still sends a signal.
I hope the whole nation shifts my way, and in case there's any doubt or claims of fraud, I want it to be seen that my area shifted the same way too. It makes lies about fraud that much harder to support.
Voting is the best bang for your buck to make your opinion known. Granted, if you openly campaign or start an organization, you might have more influence than voting, but these things require much much more effort. Voting is very efficient and worth the small effort required.
Nothing says F U to politicians quite like voting against them every time. There are some people I want to say that to. You probably do too, so vote.