I have been shooting Timelapse Motion Control for over 3 years. I teach Timelapse filmmaking in Joshua Tree, so I see, and use, a lot of 'timelapse' equipment - in the field.
here are some of my timelapse accessories
One of the essential components of timelapse is the intervalometer. You know your a timelapse guy when you can pronounce it without thinking:
IN - TER - VA - LOM - E - TER
While some cameras (Nikon) have built-in intervalometer functions - and they can even generate the timelapse sequence in-camera, it is best to manage this function outside the camera where you have more control and you can make adjustments on the fly.
This is a great little 360 degree panning head. It's super lightweight and great for backpacking. Its's controlled by your iPhone (Bluetooth) with a great user-interface. It charges with USB power, or you can power it with an external USB power pack
Battery grips are essential for Timelapse sequences that can take 3-5 hours. Most grips hold 2 batteries, so you get twice the running time of the camera.
Extra batteries are a must, and while it used to be taboo to get third party batteries for your camera, these days it's OK! After 3 years of using these batteries - and canon - the only batteries that have failed are the canon batteries. And the price includes another charger!
Getting the camera in position for a timelapse sequence can be a challenge. The Magic arm is just that - MAGIC! It allows you to get the camera into just the right position - and it stays there!
The 'standard' for full-featured timelapse Motion-Control, the second shooter is a robust, expandable system that is relatively portable. It's great for video production as well.
The "TLS" system is an entry-level motion control designed explicitly form timelapse scenarios . It is less expensive, but still uses the same great motor and controller as the second shooter. It weights less, and the rails come is 3', 4', 5' and 6' lengths - for those amazing timelapse sequences. It is a bit noisier, so if you are doing video, I would suggest getting the Second Shooter.