Seatbelt Laws
From LibertyWin.org
New Hampshire does not require adults aged 18 and up to wear seat belts. Punishments for minors without seat-belts apply to the driver, and are 25 dollars for the first offense, and 50 dollars for the second or subsequent offenses. New Hampshire is the only state in the USA that does not have any seat-belt laws for adults.
Pickup Truck Beds
New Hampshire also has no laws prohibiting passengers from riding in the back of a pickup truck.