If You Must Vote on Touch-Screen and Your Vote Flips...
Try to capture it with your cell phone camera
Call poll supervisors to observe the problem.
Fill out a problem report.
Refuse to vote on that machine.
Request that the machine be taken out of service.
Get the serial number of the machine if possible (may be difficult in some cases).
Tell other voters in line which machine it was and that they should NOT vote on that machine!
Report it to county/town election office.
Report it to the Secretary of State.
Call local reporters and tell them the story.
Call 866-OUR-VOTE and tell them.
Contact bloggers and Election Integrity websites.
Raise holy hell.