Here’s a little product that I’ve been using for a long time now. It’s called a Popout Map, a self contained, pocket-sized map with a patented folding mechanism. Admittedly they are not the most detailed maps around but conditions don’t always allow for the unfolding, reading and attempted refolding of enormous maps. For such occasions and for quick position checks, these little guys come in very handy.
These maps don’t cover every city. Have a look here to see if the one you want is available: