I leave more iPhone chargers in hotel rooms than rockstars leave broken TVs. That means I'm constantly looking for one and jumping a the chance to buy a few on the cheap. Right now, Amazon has a . That's 20% off the normal price, plus they'll ship to you with lightning speed too. Same-day delivery on orders over $35, in fact.
Two quick notes: These are not Apple chargers but they are MFI-certified meaning they are guaranteed to safely and quickly charge iPhones and iPads. The cords are also on the short side at 3 feet but still plenty long to reach up to your desk or couch as long as the outlet is nearby.
Caveats aside, we're talking three complete chargers (cube and cord) for about $4 each. Throw one in your carry-on and another in the car glove compartment. They'll be good to have when you really need them.