Having a telescope and a telescope mount is a nice start, but it is only that. A lot more is needed in order to be able to observe or image the night sky.
I have categorized them into 3 groups according to how critical they are for an amateur astronomer. Not a perfect way to group them though:
- Power supplies are essential for astrophotographers, but not always to observers.
- Astronomers using a Dobsonian telescope probably do not need a level and a compass.
But I hope the categorization below works for you.
By the way, let me know if you think I should anything add-ons to the list!