The big picture: If you're after something a bit larger (and conversely, not quite as portable), LG's new Neo Art Portable Monitor may be worth a look. It's a 27-inch display that's also powered by a single USB-C cable although it's only a prototype for now.
Having additional real estate can be an invaluable resource when working or gaming away from home but toting around a standalone monitor usually isn't feasible. This was the inspiration for Razer's Project Valerie, the triple-screen laptop prototype shown at CES 2017, but as is the case with most of Razer's prototypes, it never materialized into a consumer product.
Fortunately, products already exist to make mobile multi-screen setups a reality.
Lapscreen is a 12.5-inch USB-C monitor that connects to your computer, phone or tablet using a single cable. It measures 11.1 inches x 8.3 inches and tips the scales at around 400 grams, or 0.88 pounds. The 1080p panel is also incredibly thin, measuring just 4mm at the top and 8mm near the bottom where the connectors are housed.
Speaking of connectors, there's also an HDMI port should you prefer that instead of USB Type-C.
As The Verge points out, the Lapscreen does have one major shortcoming in that there's no built-in stand. You'll have to get creative when it comes to propping it up. Also, at just 4mm thick, I'd be at least a little concerned about the prospect of it surviving unscathed in a laptop bag.
The Lapscreen is available to purchase as of writing from distributor Faytech for $200.