Purchased my RX100 and I'm trying to make the most out of it. I got it with this bundle that comes with a spare battery, a carrying case, some film screen protectors, table-top tripod, a usb card reader, and an OEM Sony 32gb card (the real winner of this bundle, retails at $25). And all this you can get for the same price you would buy the Sony RX100 standalone for.
I also picked up this pack of spare batteries and a wall charger which works great. There may be better out there, but this fit in the budget and does the job well.
Favourite gear addition to the camera is this jacket case. Gorgeous and holds the camera in place, adds a little bulk, but I like being able to carry it around knowing that it's not getting dinged up. Can also strap it around my neck if I'm walking around bitten with wanderlust and want to journal it.
Now, I'm considering getting a screen protector and maybe a polarising filter, but I'm not sure that I need it. Besides I want to keep this as minimal as possible.