Anker now adds a whole two watts to its smallest USB-C charger, the PowerPort III: the compact charger can now handle 20 watts of charging power.
This should provide excellent power for all smaller mobile devices such as iPhones and iPads. Even for the operation (not necessarily charging – or also, just not simultaneously) of a MacBook Air, the small power supply should be sufficient, if you don’t have something more powerful with you.
For those who don’t care about the last grams, but still want an incredibly small charger that can officially charge a MacBook Air with 30 watts, the Atom PD1 from Anker is the right choice. It is only slightly more expensive, but offers you 50% more charging power.