Re the sugar - good way to tell is to read the nutrition panel, in individual serve column. It will list carbohydrates (which includes sugars) and sugars. 5 grams of sugar = a standard teaspoon (roughly).

So, to use Nutrigrain as an example, a 1 cup serve contains only 20 g of carb, but fully half of that 9.6 g is sugar (2 teaspoons). So you're not getting much healthy carb for the amount of sugar you're eating (and virtually no fibre), and because there's no fibre in it, it's not very filling so many people eat far more than 1 cup in a sitting.

Reminds me, I bought a clear spring water drink today, thought it was like one of those very minimally sweetened/flavoured ones, but then read the label and it had 25 grams of sugar!! Looked exactly like the competitor's product that has less than 10 g of sugar.