I find my iPhone makes traveling so much easier and would never leave it at home. I don't buy a lot of data, I don't mess with the SIM cards.
First and most important I have PocketEarth and download all the maps I need long before I go. These are instant loading maps that you can add locations to like where you are staying, places you want to visit, the rental car pick-up and drop-off locations, the list is endless. While traveling I pin my location as I'm parking the car so as to find it more easily and I pin the places I eat that I like so I can find them next trip.
Not having to download maps helps in two ways, you don't have to buy data and you don't have to wait for downloads. For example in Venice last year there was little to no connection available so even if you were OK paying for map downloads it took forever or just failed, PE was instant.
For driving in Europe we use a basic GPS that we got the Europe maps for and that is a more practical way to navigate while driving, but in cities when the going gets tricky we use both, the GPS for directions and the iPhone running PE for a bird's eye view of location relative to the destination (hotel usually). Very often the GPS will order a turn you can't make and then you have to wing it, and trying to make sense of where you are and where the hotel is from the turn-by-turn instructions just doesn't work so we shift to the iPhone.
Data- it is possible to travel without using any data at all but easier with some data, which we use for things like researching hotels a day or two out, we prefer traveling without pre-booked hotels or a schedule. We just spent a month in Spain with two weeks in a car, we bought 120megs of data and used 110 of it, well worth the $30. This is only possible if you can stay away from Google Maps most of the time so again a built in map is required.
As we plan the trip I place a trip sub-folder into my Travel folder in my email. In the Travel folder I have sub-folders, Spain, Yelapa, Italy 2015, NYC Thanksgiving, etc. Each represents an upcoming trip, and I move all the emails and confirmations associated with that trip into the folder. If someone suggests a place or other tip I email myself the info and move that into the folder as well. All the important stuff gets printed as well but the Travel folders allow me to quickly look things up and serves as a convenient back-up.
I hope someone can find some of this useful.