Going from the bottom of your car to your rooftop. If you are driving around with a roof rack and box that is not in use, consider storing it away until you need it. Driving around with those additional accessories will cause additional drag which will impact fuel efficiency.
The same can be said for rooftop bike carriers, although it would be safe to assume you won’t be taking a bike needlessly. In the same vein as avoiding drag, also prevent having a boot full of your possessions.
If they are core essentials, keep them, but that golf set you might use 4 weeks from now can be stored away elsewhere. The less you load up the car and remove drag, the less fuel you are wasting, plus it might even lengthen your engine life as well.