Agreed. Doing a bit of calorie counting myself at the moment and some of the things I eat / drink don't exactly make it easy at times! As you say, some detail on 'per serving' but a 'serving' is 1/5th of what's in the packet etc.
A clear indication of how many calories you are eating / drinking if you have the ENTIRE thing would be good - and potentially off putting in some cases. Though I tend to do it less now, it was not unknown for me to eat an entire takeaway pizza at a time without thinking much of it - I now see that eating such an item would use up about 75% of what I needed, calorie wise, in the day! It's certainly made me think twice about eating such amounts now and I go for either sharing the pizza or getting a smaller one instead.
So maybe price is not the only motivator.