If your bag is small, you can gate check it for free
Don’t go lugging an oversized suitcase filled with a whole semester’s worth of clothes through TSA or anything, but if you’ve got a small- or medium-sized bag you’re willing to part with for a few hours, taking it to the gate and volunteering to gate check it can save you a bag fee. It also earns you goodwill with the flight crew, as you appear to be sacrificing something for the good of the plane, even though you’re just being cheap.
HOWEVER, don’t try this if you’re flying Economy Plus on a legacy carrier -- you’ll pay an administrative fee of around $50, as well as the checked bag fee, to make this happen. Obviously, this also won’t apply to airlines that charge for carry-on bags.
If the plane sits for three hours, you can hop off
During a lengthy tarmac delay in the US (upon either arrival or departure), the DOT says an airline can’t keep you on a plane for more than three hours (on a domestic flight) or four hours (on an international flight) without allowing you to get off if you wish. So no, playing Transformers: Age of Extinction again as in-flight entertainment isn't gonna cut it. Also, the airline is obligated to get that food and water cart running down the aisle after two hours of delay.