I agree with both of those...I also have a light meter app - never had need to use it but it is one of those nice to have just in case...another is Nikon Manual Viewer which allows you to have manuals for all your gear (camera or flash) on your phone or pad...I've used those a few times when I wanted to look up how to do something I don't do that often...
Informational, there is a Nikon Lens app which basically just gives you specs on lenses and links to reviews...might not be too useful...also a Learn and Explore app from Nikon that might be nice for some reading if you want to read from phone or pad...