There are several items that are not allowed to be taken on airplanes, including: 1. Firearms and ammunition - these must be checked at the airport check-in counter. 2. Knives with blades over 6 inches in length or any other sharp object. 3. Liquids, gels, pastes, etc. in containers larger than 100 ml (with some exceptions). These must be placed in a transparent, sealed bag and presented for screening at the security checkpoint. 4. Oxygen tanks and other breathing equipment. 5. Electrical or battery-powered devices that may interfere with the aircraft\'s systems, such as lasers or hoverboards. 6. Explosives, firecrackers, etc. 7. Live animals (except service animals). 8. Items that violate import/export regulations of the destination country. 9. Items that are considered dangerous goods, such as flammable liquids, corrosive substances, oxidizing materials, etc.