I picked out a part list to make it a real tablet (if you could find similar parts for cheaper reply with links to them (no ebay))

Battery https://www.adafruit.com/product/353

Battery charger https://www.adafruit.com/product/2465

Speakers https://www.amazon.com/dp/B01JS6QHWQ

Display https://www.amazon.com/dp/B01IH6ZWWO

Raspberry Pi https://www.amazon.com/dp/B01C6FFNY4

And Cellular NeeCoo Bluetooth V4.0 Dual SIM Card Adapter-29.99 Online Shopping| GearBest.com