Besides photo storage is use my iPad for various other reasons on my trips.
Following software is installed
LightTrac: Enables me to track the position of the sun in any specific place, time and date in the world. Nice to see where to stand to make the best pictures. Especially handy for outside museums.
Goodreader for iPad: To store (externally on server space) and view various PDF documents regarding spottersplaces, etc.
Bento: To access my database containing all the books in my collection, when shopping
Filemaker Go 11: to view the extensive roadbooks for long trips. To see info on museums (opening hours, contacts, etc.)
Always handy to have access to these items when no internet is available.