Mobile devices are nice, but having travel information when there's no Wi-Fi is even nicer. Last week, travel site TripAdvisor (NASDAQ:TRIP) rolled out a tool that lets app users download city guides while they're connected and then refer to them offline. For anyone who's ever been hit with unexpected data roaming charges on a trip, or worse, ended up with no access to the information they needed, this is a welcome feature.

The new "downloaded cities" tool offers maps, plus data on hotels, restaurants, and attractions for some 300 U.S. and international cities, such as London, New York, Rome, and Dubai. When users look at their downloaded city information offline, they'll be able to see 10 reviews per attraction or hotel. The company promises more destinations to come, and the new feature is already available everywhere TripAdvisor's app works -- and in all its supported languages.

As far as big-city data for travelers goes, this looks like the app to beat. But other companies offer offline value in their apps, too.

Carrier contacts, currency, and seat configurations offline
Kayak, the travel booking comparison site owned by Priceline Group (NASDAQ:BKNG), offers an offline list of contact numbers for many airlines along with suggested packing lists for different types of trips and a currency converter -- all available without having to download anything in advance. With a wireless connection, Kayak's app also shows terminal maps and amenity information for dozens of airports. It would be handy if that info could be downloaded for later reference offline.

Quicket, a popular app from Kwiket GmbH of Munich, lets users search for flights and buy tickets on short notice with a Wi-Fi connection. But the app also offers a treasure trove for flyers who don't want to book seats next to the galley or the restroom: offline seat maps for dozens of domestic and international carriers. Flyers can also search by aircraft to see common seat layouts for Airbus and Boeing jets. Quicket says the seat information is always being updated.

Finding the way and speaking the language
Anyone who's ever gotten lost in a strange place will appreciate the offline function that Google (NASDAQ:GOOG) Maps launched for Android and iOS in May. Like TripAdvisor's offline city guides, Maps' offline tool requires users to plan ahead and download maps. But then they're available for reference, no matter how many hills, tall buildings, or sprawling acres of pastureland are between the user and the nearest tower.

Google had already made its Translate app workable offline for selected languages with its Android 2.6 update in 2013. Users who want to communicate offline will need to download the language pack they need ahead of time, and it's worth checking well in advance because not all language packs are downloadable. Hindi and Spanish, yes. Tamil and Basque, no. Also, the language packs are large -- our recent Spanish download totaled 242 MB of data. That's definitely something to take care of over a home network instead of while roaming.

These features all add up to potential data-plan savings for travelers, especially those who go abroad frequently or for long stretches of time. They can take some of the stress out of being "out of range" as well -- as long as there's a way to keep the phone charged. And they will probably create the expectation of more offline features to follow from these companies, their competition, and independent app creators.