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) lenses of widely spaced focal lengths:
1) a wide-angle lens. I recommend one of approximately 20-21mm 'FF' eq. (which translates to ~14mm if using APS-C cameras, and ~10mm if using m43 cameras). This gives a 'bold' perspective that's wide enough for most uses, yet still without being too extreme;
2) a fast 'normal' lens of approx. 50mm 'FF' eq.(~35mm if using APS-C cameras, or ~25mm if using m43 cameras). A supremely versatile focal length, which IMHO should be used 'by default', unless there is a good reason for switching to one of the other two;
3) a medium telephoto lens. My favourite focal length is the 'classic' 135mm 'FF' eq. (~90mm if using APS-C cameras, and ~70mm if using m43 cameras). This gives enough 'compression' to clearly differentiate itself from the 'normal' field of view, but is still short enough to be conveniently hand-holdable.
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'.