The list of items prohibited on an airplane varies by country and airline, but in general, the following items are not allowed in carry-on or checked baggage: Weapons and self-defence items, sharp objects, flammable materials, explosives, toxic substances, or liquids over 100ml (except for medications and baby essentials). In checked baggage, firearms (without authorization), explosives, large lithium batteries, and hazardous chemicals are prohibited. Electronic cigarettes must be in carry-on bags, while alcohol and dry ice have restrictions. Always check with your airline for specific regulations.