Sport equipments, such as bycicles, surfboard, skis can be carried in the hold, according to the airline procedure, registered at check-in and sent through a dedicated gateway.
Bulky baggage, such as musical instruments of big dimensions, has to be placed in the seat next to you. Therefore, you need to book and pay for an extra seat. Check with your airline for weight and dimensions.
If you carry firearms and ammunitions, you must follow specific instructions and be in possession of the documentation certifying the possession.