I carry the G4 spare, a slim profile 5000mAh extended battery with built in micro usb, a 12000mAh extended battery, a micro usb cable and a micro USB plug to lightning adapter. Between, my G4, 2 iPhone 6 Plus, 2 iPad Mini... there is always 1 or 2 devices need juice when we are out.
I guess it depends on how much you drain your battery during the day. I charge my G4 over night every night. So I always start out full... so I rarely need to swap to the spare on a regular day. On vacation, when I use the GPS a lot and the camera... I will need to swap out by the evening, but never had to go to the extended battery for the G4. I now carry the extended batteries pretty much for the iDevices in the family.