Charcoal

Allowed if it's plain charcoal. Ordinary charcoal briquettes or lump charcoal with no lighter fluid or other accelerant added are generally permitted in carry-on bags. Because loose charcoal is a fine, dusty solid, it can trigger extra screening, so keeping it in a sealed bag or its original packaging helps it move through the X-ray without a hassle. Quick-light or self-igniting charcoal — pre-treated with lighter fluid — is not allowed in carry-on, since the added accelerant makes it a flammable hazard.

Allowed if it's plain charcoal, and checked baggage is actually the better place for it — TSA and most airlines recommend packing charcoal in checked bags rather than carry-on to avoid extra screening delays. Quick-light or lighter-fluid-treated charcoal is prohibited in checked baggage too, since a flammable-treated solid is banned regardless of which bag it's in.