OK, you're probably not going to actually take a shower with a portable SSD drive, but you could if you wanted to with Sandisk's latest since it's waterproof. The Extreme 510 portable SSD is the follow up to the already announced Extreme 500, with the new IP55 rated water resistance one of the headline features.
Besides size, one of the benefits to carrying an SSD in place of a portable hard drive is data transfer speeds. The Extreme 510 boasts 430MB/s read speeds and 400MB/s write speeds, both of which are pretty handy if you're carrying around a ton of large files.
Which you can totally do since the Extreme 510 is available in a 480GB storage size, while still maintaining the form factor and durable design of its predecessor. And SanDisk SecureAccess software makes it easy to create password protected folders on your drive. The connection is microUSB 3.0, but you do at least get the cable included in the package.
It isn't cheap, and if you're wanting one you'll be putting down around $250. But you can take it in the shower with you, so there's that.