The combination cap that McGarrett is holding at the end at the Five-0 headquarters is the wrong one according to his rank in the United States Navy - he is a Lieutenant Commander in the Naval Reserves and the cap is for a full Commander [indicated by the gold oak leaves and acorns on the visor]
When the team enters the hotel elevator pursuing the injured suspect in the kidnapping, McGarrett racks the slide of his handgun to load a round in the chamber, meaning that the weapon was unloaded. While this is a common instrument to enhance dramatic effect in movies and television, it is completely fictitious. Police officers do not carry their sidearms unloaded.
Whenever they are seen inside Dano's Camaro the door locks are shown in the up position. They automatically lock into the down position when the car reaches 10 mph, and could only be up if someone manually pressed the unlock button located in the center console (between the air handling knobs) while the car is in motion already.
Danny says to Steve that he emptied a mag(magazine) into Victor. But at the end of the previous episode when Steve shoots Victor he only shoots him two or three times.