The sun hood is a must have. Also depending on your budget a good case. I bought a case from mc-cases and use it for storage. I also have a tail bag on my motorcycle with custom fitted high density foam so I don't have to carry it in a backpack. Also I'll be getting a regular backpack custom fitted when For when I travel. For me it's all about convenience... I wanna be able to transport my Mavic in the most safest and convenient way possible. But as far as accessories. Extra batteries, props, charging hub (pretty much everything in the fly more combo). Lastly deciding what device you're going to use with your rc. I tried using my iPhone. But it's a pain having to take it out of a otter box case every time. So I use an iPod touch. Some people prefer an iPad mini or some sort of tablet, but I like everything compact.
Hope this helps.