Nice bike, OP.

My must-have accessories, in no particular order:

1. Helmet (okay, that actually is first on the list).
2. Clipless pedals / shoes.
3. Bar ends.
4. Saddle bag.
5. Front and rear lights.
6. Bike computer / GPS
7. Twin bottle cages / bottles.
8. Cycling gloves.
9. Cycling shorts / bib.
10. Multitool.
11. Floor pump with dual head.

I may be forgetting something , but that's more or less it. Pretty much the same mix for my road bike, with some swapping.

Peeps are probably sick of this pic already, but whattheheck: