To spend a large portion of the day downtown, or in another area abundant in coffee shops, visiting as many coffee shops as possible. When coffee hopping, one buys a small coffee/pastry, spends some time in a coffee house, then moves on to another coffee shop to pass the time. (Can also be defined as attempting to sit for as long as possible in a coffee shop without purchasing anything, then moving onto another place when the barista is on to you.)
Tom: You were downtown for 16 hours? What'd you do the whole time?
Jerry: Coffee hopped.