According to
this article, and extrapolating forward another several years, the number is likely to be somewhere around 140 million. Given some average book size ranges and standard text compression factors, that would take around 1.2 - 1.5 petabytes of storage space.
The biggest USB memory sticks available now are 1 TB, so you would need well over a thousand of them. How big are your pockets, and will you be needing to walk around with your library? Another option would be to go to
this vendor and find out how much the 100 TB SSD costs (they don't publish the price, but the 64 TB model will only set you back 16 large). You'd only need a dozen or so, and they're 3.5" form factor so you could conceivably cram all of them into the available pocket space on a good pair of cargo pants.