Keep in mind that most airlines require that you check in at the gate at least 10 minutes before your domestic flight. If you don't meet this requirement, the airline is not obligated to give you a dime in compensation. By regulation, the airline must seek volunteers before they deny boarding. If you get to the gate within the check-in limit and you're told the flight is full, remind the gate agent that they are obligated to board the aircraft and ask for volunteers before they deny you your seat. Domestic bumping minimums are set by the U.S. Department of Transportation and stringently observed by the airlines.
International travel is a little more complicated.
International flights departing from the United States require the same compensation, but the airlines get a little more latitude. If you're bumped on a flight departing from abroad, you're subject to a web of rules that vary by country. Airlines flying from many other countries offer far less. Some offer nothing at all. Generally, the compensation holds value for one year.