Weigh or volume measure the carb-containing contents of your snack packs. Personally I wouldn’t bother with the carbs in nuts for a smallish serving, but everyone is different. You need to know the total carb value for the amount of raisins and dried cranberries you’re using. Mix everything up with the nuts and either (a) divide the total carbs by the number of bags you fill, or (b) divide the total weight (or volume) by the weight (or volume) of your serving, and derive the carbs from that.
method a) total 200 g carb divide by 20 bags = 10 g per bag
method b) total 10 cups mix divide by 1/2 cup servings = 200 g carb divide by 20 servings = 10 g per bag
If you’re going by volume rather than weight, I’d use a measuring cup rather than the markings on the bag. The markings won’t be too accurate, depending how packed in the contents are.