When I bought my android phone, the accessories I chose for it were a sturdy case (I’d heard all those stories of what happens if you drop your phone) and a set of lenses that attach magnetically to the camera lens.
The latter turned out to be fun, and they do get used every so often.
Here is a tiny sample of what they can do, showing images using the fish eye and wide angle lenses. There is also a macro lens.
They were fun to use, and could prove useful in situations where a digital camera just can’t capture certain features. I just have to remember to always have the lenses in my pocket when I go out, and then also remember to use them!