I have a Rapid Transit Recon 19 tank bag. I made two modifications... took a soldering iron and burned a hole just above the right front corner, from the inside to the rain cover compartment and then through to the front, and then put another hole at the back of the cell phone pouch. I run a short SAE 4-1 splitter into the bag, then hook up feeds to my GPS and GoPro back out through the hole, and to another USB power converter that runs to a 4-port hub. I charge my tablet and phone and GoPro wireless remote from the hub, and run the phone USB cable through the factory wiring hole and then up to the cell phone. I leave the phone compartment partially unzipped to keep phone temps low. I also run a Camelback bladder in the bag. My sunglasses and wallet fit in the side pockets.
Having water, power, a phone (via Cardo helmet-mounted headset), and GPS keeps me on the bike and riding. Some Power bars or beef jerky and I can ride for a tank without stopping... about 240 miles, for me.