Rockpeter, as far as the coffee shop owner worrying about you using the table - just ask them. My guess is that it depends entirely on how much business they have. If all tables are being used because they are busy, they likely won't want you taking up a table for a couple of hours. But if they never get more than 1/2 their tables full anyway during the time you are wanting to use it, then I doubt they will mind.
I suggest you bring a chess book, set up a board, start working through some things from the book. If nothing else, that gives you something to do while you wait hoping for a game, and if nobody asks to play, you haven't completely wasted your time. If you really want to find someone to play, make up a small sign saying "Want to play a game?" and set it on the board. Some people may not want to ask, asuming you're studying the book or waiting on a friend, but the sign will make sure they know you would like to play.
I've done this in bars a number of times. I use a small magnetic set to set up positions from a book, but keep a full sized set available for anyone that wants to play.
I was wondering myself while walking the mall last week. There are many coffee shops now in the middle of the mall and I see some people alone reading a paper or just having their coffee. I wondered what would happen if I just brought a board on the table with my coffee if I would have players come and want to play. I don't have the guts to do that sort of thing but it did cross my mind. And maybe the owner wouldn't appreciate taking a table for so long.....unless I kept drinking coffee
And although I am a club member, I was wondering if putting an ad up in the supermarket to find people for friendly matches was a good thing. This because at the club we play rated and I am basically playing the same individuals every week.