In Sci-Fi, it's normal to see landscape displays on forearms. Often it's part of a suit, so it is kind of an obvious solution. But watches could take this concept at a smaller scale and provide at least double the screen real estate without ending up looking like a brick.
The bands on some watches are already fairly thick, and people have shown they are fine wearing thick bracelet things for decoration. Why not embed batteries into parts of the band? The obvious case would be the big metal links (like tank tracks), with the wiring through the link connections. Not only would you be able to store a whole lot more energy compared to a single battery in the watch body, but you could also have swappable bands so you could always have one charged and ready.