A short list of items never flies as baggage in any form: fireworks, most flammable liquids, bear spray, loose lithium batteries over 160 Wh, and anything that counts as an explosive. A longer list is checked baggage only: firearms in a locked hard case, ammunition in its box, tools, and self defense sprays under the size limit.The line between restricted and banned moves with the airline, the country and the officer. Each item page below states the federal rule, then what airlines add on top and how the rule changes once you leave the US.