The only 2 places I ever park my bike and take my eyes off of it are at work (security guard only allows employees in plus we have cameras in the parking lot)and at home (shed with 3 locks plus the Kryptonite chain -not cable- on bike).
I never ride to a location where I can't see my bike. If I ride to a restaurant, I always request a window seat and once I'm seated, move my bike as close to that window as possible. Even on that note, I have been riding for 3 years now and have riden to a restaurant twice.