I have a couple book packs and a small Ameribag, all of which are under-seat carry-ons. All have stash pockets. So with more than 1 watch, the extras can go into a watch wrap or case, and if preferred, the worn watch can be slid into a stash pocket.
I wouldn't worry about the magnet in earbuds at all; should be too small. Fuller-size headphones like Beats might be an issue. A magnetic tablet cover *can* be an issue. I have a Portenzo cover for my Nexus 9, and yes, it's made a couple of my quartz watches run very off while they were too close.