Steps on every surface
Footsteps are the most-requested foley sound in film and games because they are everywhere and hard to record cleanly on set. A useful library covers several surfaces, such as wood, concrete, gravel, grass, snow and metal, and several paces, from a slow walk to a sprint, ideally with each step separable.
Recording quality to listen for
Good footstep recordings are close and dry, with little room sound, so they can be placed into any scene. Listen for consistent spacing in a walking loop and for the shoe: heels, trainers and boots sound very different. For games, longer takes with many distinct steps are worth more than a short perfect loop.
Foley recordists often release their work under CC0 or CC BY on Freesound and Wikimedia Commons, and many game audio packs, such as Kenney’s, are CC0. The verdict on each card tells you what applies.