My rules world-wide:
1. Declare any food or beverage substance (chocolate, jam, teabags, coffee beans...) (I draw the line at things like chewing gum or breath mints, though.)
2. Be prepared to be accused of wasting their time, for which I will offer my profuse apologies.
Lather, rinse, repeat.
Seriously, you can't win this one.
My honest-as-the-day-is-long young colleague was mercilessly excoriated at SYD for not declaring a (commercially packaged) box of tea bags from the UK. In his mind, tea is a drink, not a food, and the bags aren't even a drink until you add water. They let him keep it, but he was extremely - and unnecessarily - embarrassed.
At the same airport, I regularly declare Swiss chocolate. 20% of the time, I'm told "you don't need to declare that". 20% of the time, they ask to look at the package to "make sure." 60% of the time, I'm told "Okay, no problem." One time they located it on the (random) baggage x-ray (I had declared it) and asked me to get it out. I pulled out a flat gift-wrapped box, they glanced at it and said, "Okay, fine." There's no rhyme or reason.