Items not allowed in a plane carry-on generally fall into categories of weapons, explosives, flammable substances, and hazardous materials. Key prohibited items include:

• Weapons and related items : Guns, firearms of all types, toy or replica guns, firearm parts (except telescopic sights), compressed air and CO2 guns, bows and arrows, slingshots, brass knuckles, knives (including pocket knives and Swiss Army knives), razors, and self-defense sprays such as pepper spray or mace are not allowed in carry-on bags

• Explosives and flammable substances : Ammunition, blasting caps, detonators, mines, grenades, fireworks, flares, smoke-generating canisters, dynamite, gunpowder, plastic explosives, flammable liquids (petrol, lighter fluid, alcohol over 70% volume), aerosol paint cans, gas bottles (butane, propane), and oxygen gas in large volumes are prohibited in carry-ons

• Chemical and toxic substances : Disabling sprays (mace, tear gas), acids, alkalis, corrosive substances (mercury, chlorine), fire extinguishers, infectious materials, poisons, radioactive materials, and toner cartridges cannot be carried on

• Liquids, gels, and aerosols : Liquids, gels, creams, and aerosols in containers larger than 100 ml (3.4 oz) are not allowed unless they fit within a single 1-liter clear plastic bag and meet specific exceptions for infant formula, medicine, etc.

• Sharp objects and tools : Scissors with long blades, axes, hatchets, baseball bats, crowbars, drills, and other sharp or potentially harmful tools are banned from carry-on luggage

• Other prohibited items : Fireworks, Christmas crackers, smoking/vaping devices must be carried on with restrictions or packed in checked baggage; some sporting equipment and mobility devices with batteries have special rules

In summary, carry-on baggage must exclude weapons, explosives, flammable and toxic substances, large quantities of liquids, sharp tools, and other hazardous items to comply with airline and security regulations