Best Burger: Wimpy. Runners up: Most of them, but I had an amazing breakfast one at Hache.
Best Sandwich: Reheated Bolognese in pitta
Best of all: The chocolate fondant they do in Carluccio's.

p.s. this is what some musicians ate on the road http://drownedinsound.com/in_depth/4147225-tourmet-delights--the-best-things-musicians-ate-on-the-road-in-2013 (it isn't all Gregg's but they do get a few shootouts!)