We have used "3M" brand Command Picture Hanging Strips. They hold pictures to the wall securely and can be removed without causing damage. For mounting knick knacks to horizontal surfaces we use "Quake Hold" also referred to as museum putty. Again, it holds items securely and can be removed without causing damage. As for anchoring things to walls, I have used standard wall anchors for things like toothbrush holders in our current rig and a small (6-8 bottle) spice rack in our last rig. Just be aware you will be putting a hole or holes in the wall.
2018 Bighorn 3575EL (now SOB's) Residential Fridge, W/D.
2011 RAM 3500 Laramie, 4x4, SB Super Glide Hitch.