The single most important fact about Norwegian customs, and the one people most often forget, is that Norway is not in the European Union customs union. It is in the European Economic Area, which aligns a great deal of regulation, but goods crossing the Norwegian border cross a real customs frontier with real formalities in both directions. A consignment moving Oslo to Dubai is an export from Norway; a consignment moving Malmö to Oslo crosses a customs border that a Malmö to Copenhagen movement does not.
In practice this costs a step rather than a day, provided the step is taken at the right time. The export declaration is prepared before the courier leaves, the classification is agreed rather than guessed, and the value is stated in a way that can be defended. What causes delay is treating the border as a formality and discovering it at the airport.
Ship's stores and ship's spares deserve their own mention because they are so common on this desk and because their treatment is frequently different from an ordinary import. Goods destined for a vessel can often move under a specific regime, and using it correctly is materially cheaper and faster than not.
Beyond that the usual regimes apply. Medicines, biological material of human or animal origin, dual-use technology and dangerous goods each have their own authority and their own requirements, and those requirements decide whether a consignment moves at all. Aquaculture and fisheries material in particular sits under a veterinary regime that is strict and enforced.


