If you like Steak and chips - L'Entrecote, two up from the tourist office, and just down from the Opera, it is a must - you have to queue, (cannot reserve a table), but it is worth it and they can seat plenty anyway - it's not expensive
4 cours du 30 Juillet, 33000, Bordeaux - in what's called The Golden Triangle
we lived there for a few years, in BDX not the restaurant!!
shorts and shirt - not sure about the trainers!!