Welcome to FT!

Finkface, I think the technology is just one piece of this. The content is the other. It sounds like OP is looking for something all wrapped up in a nice package.

With the wireless USB drive, you still have to figure out where to get the content from. Many legal services don't let you watch offline... or if they do, it is heavily restricted. Even if you buy movies on iTunes, there's DRM. If you download it on Amazon, you may be restricted in how long you can access it offline before you have to reconnect. Those services are fairly easy to use though, so as long as you are okay living within the boundaries they set (i.e. using their app, downloading content before you travel), that may be the best option here.

Freeing yourself from these shackles and getting truly portable content is difficult. Ripping from DVDs/Blu-Ray that you already own can be technically challenging... as is sourcing content from, shall we say, other locations of a more dubious legal nature. I have no interest in discussing the latter, given forum policies, mentioning it only to illustrate that there are very few means available to people who don't have the inclination to tinker a little bit.

To directly answer what I think is OP's question: you will not find a USB drive pre-filled with content. The simple reason is that it costs too much. DVDs and Blu-Rays cost a lot less to manufacture than flash memory, so for people who need physical media, that is the format. And with internet connections becoming more ubiquitous, the focus is shifting away from physical media and towards streaming. There was a company called FlixChip back in 2012 that tried to launch USB as a competitor to Blu-Ray and streaming. It never took off... I don't think their Indiegogo crowdfunding campaign was successful.