I would invest in a second battery as back up. Then you can alternate between the two and you will never be out of power. When the battery in your camera is getting low on charge, charge up the second one and put it in your camera bag.
Another very useful tool is a memory card reader. Use this to move your images from your camera to your computer rather than the wire connector from the camera to the computer. It will save the life of your battery and wear and tear on your camera. Be sure to match the reader to the size of your memory card. Some will read only one size, others multiple sizes for several cameras.
These, I believe are two "must haves". Other than that, the sky is the limit.
I would suggest you play around with your camera pkg. as it is for a while and enjoy it before you go out and purchase extra lenses and gadgets. You will know what you want and need in time.
Have fun!