> Bike from downtown JC to George Washington Bridge and take subway + PATH back

No need to take the subway/PATH back. Just cycle the whole thing! I've done this before but started at 33rd Street, cycled up the Hudson Greenway to GWB, crossed it and then cycled back down to JC. Although the Jersey side doesn't have bike lanes so you have to be very comfortable driving among cars, or cycle slowly on the sidewalk. Another option is cycle from JC to GWB, cycle down to midtown and then take the ferry back. Ferry is more expensive than the PATH, but it's fun to do it once.

> Take the Light Rail without ever paying for the fare (no one really does and it's rarely enforced.)

It's definitely enforced, but I think they mainly check during rush hour. If you're outside of rush hour, less likely to get checked. I don't know what the penalty is if you're caught, but probably not worth it. I'd just pay.