It would be nice to be able to add a custom activity and set the calories burned. Many times I know exactly how many calories I burned based on what the machine said, but can't find an exact match in the list. Other times, my entry just isn't there. For instance, I do Yoga but the only option is Hatha Yoga, which is not the same thing and burns more calories.
DISCLAIMER: I am NOT an expert in nutrition, fitness, or exercise. Any advice given is only meant to be helpful based on what information I've gathered, and should not replace any medical treatment or any other true advice you may get from another source. Take it with a grain of salt, and then log that in your Foods tab!