Depends on how long you want to play with it on one load.
A screen like that doesn't draw that much power (the 10 inch mentioned by tikiandskull uses a 5V 2A power supply - so at its max it will draw 2 Amps - my 7 inch can be powered through a laptop USB port even). With a 20.000mAh powerbank you should be fine for 3-4 hours at least.
If you need more power you could look into something like a LiPo, but that takes a bit more work (with battery protection and such).