Spontaneity is fine when you\u2019re on a trip. But it\u2019s of little use when planning that getaway, because airplanes, hotels and rental cars are often fully booked in advance. Still, if you\u2019ve got a sudden travel itch this Memorial Day weekend, the following apps can help.\n\tCheapOair\n\tI pretended to plan a last-minute trip from San Francisco to New York for the holiday. CheapOair, a free app for iOS and Android, instantly found me an airfare on U.S. Airways for $476 \u2014 though it was for a round-trip to Newark, N.J. Still, Newark is close to New York City, and the flights were at fairly reasonable times (no red eyes, in other words). By comparison, the cheapest airfare I found on Kayak was $762, even with Newark factored in as an airport choice. Also, CheapOair\u2019s app offers 24\/7 live chat, an unusual feature for a mobile app.\n\tHotel Tonight\n\tFinding a hotel at the last minute can be a challenge \u2014 and expensive \u2014 but that\u2019s the name of the game for the free Hotel Tonight\u00a0iOS and Android apps.\n\tWhen I used the app to search for last-minute hotel deals in New York City, the best I could find was $515 at the Paramount Hotel, a discount from $595, and it was only available for the night I searched.\n\tThat\u2019s not exactly worth shouting from the rooftops, so I also tried Charleston, S.C. I could have booked one night at the Elliott House Inn \u2014 one of my favorite inns in Charleston \u2014 \u00a0for $159. Here again, the rate was only good for one night. In fact, most of the hotel deals I found were for one night only, so this might not be the app to use for an extended stay.\n\tTravelzoo\n\tThese free iOS and Android apps provide daily and last-minute deals on entertainment, restaurants, spas, various activities (such as whale watching tours and wine tasting classes) and accommodations. They're easy to browse \u2014 you can scroll through lists or see deals on a map near you. Not all the deals are available immediately \u2014 a New York City hotel offered a two-night stay for $299 (compared to $589) but was only offered July 1\u00a0through Sept. 1.