Cleaning my gym and workout gadgets; how do I do so most efficiently/easily?

I have an mp3 player case, and also a heart rate monitor I strap around my chest. Obviously after excessive use they begin to smell really bad. In my opinion I perspire more than most especially on days when pushing myself. While with gym clothes I have a good rotation to stay clean and do well odor-wise by fellow gym goers, I'm concerned with the elastic bands and rubber/plastic pieces on these gadgets I'm going to ruin them if I try to clean them the wrong way. I can't remove the fabric pieces completely alone on these items.

So r/fitness, how do you clean these items? Any recommendations?