We regularly get road dust/grime on our library material and if we carry purses/tote bags, we have dark colors so it doesn't show.
We clean out our bookmobiles 3 times/year-each for a 2 week period. We scan all the barcodes, take the materials off the shelves and wipe down the shelves, and we refresh the collections.
Idk if it is where the items are located and/or what material they're made of, but we do have to wipe down some things. You can use a glass cleaner or purell with a little elbow grease and paper towels. I'm going to experiment with a vinegar/water/dawn
dish soap spray and see if that works better. Some people use gloves to protect their hands from dying out.