But then, it's winter here.
We're in the process of purging our bad food habits, but not with promises/resolutions. We try not to buy stuff that's not good for us, and substitute as much as possible to accomodate our weaknesses. For example:
coffee -> inka (tastes better anyway, none of the nasty caffeine buzziness)
chocolate -> cocoa
ice cream -> frozen yogurt (in shakes, so we don't notice)
cheese -> older, drier cheeses so using less generates more flavour
instant noodles -> we bought a pasta maker on sale
chips -> now always plain, always served in a bowl with healthy dip (limits portion size & we eat fewer chips as a result)
Our evening snacks are now always fresh fruit, which has really helped. A friend of mine who had horrible munchies from ganja lost 50kg by switching to grapefruit and watermelon from chips and chocolate. We don't have the ganja, but we liked his idea.