For the landscape and travel photographer who wants to travel light, rather than settling for the ubiquitous, ever-wider-range (but often hopelessly slow) zoom(s), I would suggest going against the grain and starting with a small set of prime (fixed focal length) lenses:
1) a wide-angle lens. I recommend one in the 20 to 25mm 'FF' eq. range (which tranlates to 14 ~ 16mm if using APS-C cameras, and 10 ~ 12mm if using m43 cameras);
2) a fast 'normal' lens in the 40 to 55mm 'FF' eq. range (or 27 ~ 35mm if using APS-C cameras, or 20 ~ 30mm if using m43 cameras);
3) a medium telephoto lens of approx. 85mm to 135mm 'FF' eq. (i.e. approx. 55 ~ 90mm if using APS-C cameras, and 40 ~ 70mm if using m43 cameras). If preferred, this lens can also be one of the macro/micro types, which are generally of excellent quality but somewhat slower.
With these three lenses, you will have 'all bases covered' with great image quality, and will never be in doubt as to which lens should be on your camera at any given time. Even more importantly, they will spur you to 'pre-visualize' the scene, and not give in to the temptation to plant yourself in some random spot and 'frame by zooming'.
Only later, and only if more specific needs arise, should you start thinking of adding more lenses, such as, for instance, a longer tele (e.g. ~200mm or 300mm eq.), and then maybe even something more outlandish like a fish-eye or tilt-and-shift lens.