Heres what I do before a trip:
- create a label for important trip documents like reservations etc.
- Set this label to sync offline in the Gmail application (settings -> your account/email -> "Sync inboxes and labels" -> then find your label)
- create a shortcut to the label on your home screen
- download map areas to google maps (or MAPS.ME or HERE)
- star specific locations in map app (hotel etc.), either with a star or via My places for google maps
- download wikisherpa versions of wikitravel
- download trip advisor city guide if available
- install apps or pictures for subway maps
- install apps for translation (some of these have huge offline lexicons that are downloaded to your phone)
- download TED talks for watching on the plane (or other movies/tv shows)
- don't forget to pack the charger!
The first two points are the best I'd say. Having all your documentation one press away is pretty handy. Also, having internet around is always handy.. I have a shortcut on my homescreen to the wifi menu which is handy when you need to make a quick skype call.
