Since most travelers nowadays have "smartphones", it only makes sense that we should start figuring out how to use these to save while we are traveling. With that in mind (and since I work in the high-tech Silicon Valley area), I thought I'd list just a couple of the many mobile phone apps (and there are many free ones that do this) that are really helpful at helping you either get a discount or figure out where the lowest prices are in the local area to buy a particular product or figure if the restaurant/store/service is worthwhile. Some of these are:
Shop Savvy--lets you scan a price tag in a store you are in and then tells you if the product can be purchased cheaper somewhere else close by (nowadays if you show this to the checker at the store you are in, many will match the price--meaning you don't even have to go to the other store)
RedLaser--finds the lowest price for a particular product within a 10 mile limit of where you are currently located
Similar apps (although I don't know if these are free or charge a fee) are Foursquare and Loopt.
Facebook pages of Retailers sites--almost always offer discounts--this can be accessed via the mobile app or the regular facebook page.
Yelp--provides reviews of the local merchants/restaurants/service providers you input. This is especially helpful when planning where to stay or eat or visit.
Coupon Sherpa or Yowza!--these two free apps provide online coupons on your mobile phone that can be scanned and redeemed while you are still in the store (they just scan the coupon on your mobile phone and give you the discount). Groupon is similar--but I believe they charge for their app.
AmazonMobile--if you are in a store and wondering if you can buy the product cheaper online (via Amazon), here's the site that allows you an easy way to check
CompareMe--this allows you to check which is the better deal on two competing items (for example different cereal boxes in a store) if the two items weight different amounts or have different number of contained items
MySimon--compares items across online shopping sites to tell you where you can buy the product for the cheapest price.
Twitter--download the app, then use it to check tweets at @FatWalletdeals, which tells the best deals being offered by retailers for the day or week (for example, which ones may be giving 15% off and which ones may be offering free shipping anywhere in the world)
And, of course, almost all the major airlines now have apps that keep you informed of latest flight changes (including boarding/departing gate changes), and of weather delays on their flights
[ Edit: add Twitter FatWallet option ]