If it's sufficiently fast and has a screen, someone will eventually get an old-school game emulator running on it. Over the weekend, iOS developer Gabriel O'Flaherty-Chan made that happen for the Apple Watch with a Game Boy emulator he calls "Giovanni."
Named for the leader of Team Rocket from the original Pokémon games, Giovanni runs Game Boy and Game Boy Color games on the Apple Watch Series 2 (the Series 1 hardware is presumably capable of the same performance, though the original Apple Watch is likely too slow). O'Flaherty-Chan used the existing Gambatte emulator as Giovanni's core, and then added Apple Watch-friendly controls. There's room for the select, start, and B buttons at the bottom of the screen; you tap the right side of the screen for the A button, while the left side of the screen is mapped to the control pad. Turning the Digital Crown up and down can also simulate the up and down buttons on the control pad.Here’sPokémonYellowrunningGameemulatorAppleWatch