JackeryAir external battery – $60
Mobile technologies require batteries, that's a fact of life. External batteries are especially important because in 2007 Apple decided that gadgets could be smaller and thinner with a fixed (non-removable) battery. It started with the iPhone, and later spread to the iPad and MacBook too. Without the option to swap in a second battery, mobile technologists need to keep a charged battery nearby.
The world's thinnest portable charger is JackeryAir ($59.99, Amazon) which measures a svelte 4.9 x 2.3 x 0.3 inches and weighs only 5.4 ounces. It's almost the exact size of an iPhone 5 and could hide directly beneath it. In fact, the world's coolest battery would be an inductive JackeryAir that I could attach to my iPhone 6 (Cupertino: are you paying attention?). Anyway, I digress...
The JackeryAir packs 5,000 mAh of juice which will charge a dead iPhone 5s just over three times and it's made of aluminum for that high-quality feel. There's also a status LED, which indicates how much power remains.
Honorable mention: RAVPower Luster battery is a compact, lipstick format 3,000 mAh external battery that features an ultra bright LED flashlight. It comes in gold (to match the iPhone 5s) and it's on sale at Amazon for only $19.95.