1. Frozen yogurt: While this can be a slightly healthier alternative to ice cream, that is what makes it dangerous! We tend to eat more when we know its "healthy-er". Keep your portion small and limit your toppings to one favorite!
2. Popcorn: I too am a fan of all the delicious popcorn flavors you can find everywhere nowadays, and while popcorn is far better than chips or pretzels, it can still be overdone. While popcorn's nutritional stats are decent, it goes down easy and by the handful. Topped with some artificial butter or cheese powder, it can pack a punch of calories without you even realizing it.
3. Peanut butter: Yes, a wonderfully healthy source of fats, fiber and protein, it is also very calorically dense and the serving size can disappear alongside crackers or veggie sticks with two bites. Portion it out ahead of time to be sure you know how much you are eating.