Bhutan features rigorous regulations in customs. One of the important regulations include receiving a baggage declaration form to complete when you arrive at Bhutan Paro airport. It is mandatory not to lose the form as it is required to be returned while leaving Bhutan. The main purpose of this form is to ensure that you should take back anything that you bring into the country. Expensive items that you may be carrying such as cameras, phones and laptops need to be declared. If you are carrying equipment for commercial filming, then that would require a permit that the tour operator will acquire for you.
As you may have heard Bhutan has a strict anti-smoking policy and cigarettes are rarely available and expensive inside Bhutan. This can tempt you to bring in cartons of your favorite smokes in your luggage. However, customs regulations ensure that only two cartons of cigarettes/2 boxes with 50 pieces each can be brought inside Bhutan, but 200% duty will be charged on arrival at Paro.