I know you shouldn't go food shopping when hungry - but I went straight from the gym - feeling all smug I'd worked hard, hair still wet, I found it impossible to put anything fattening in my basket, it just would have made the last 2 hours (and my precious morning off) pointless.
Mind you if I only went shopping after the gym i'd starve and definiately lose weight as I don't go regular enough - but its my dieting tip!!