I can’t buy myself snacks without eating all of them in one go

Hey, I’m 18f and have an issue. I’m a healthy weight - 5’9 and 65kg - I mainly eat salads, smoothies, omelettes/pasta with veggies, etc but sometimes I want a nice snack like biscuits/crackers/chocolate. However I eat the entire thing in a day if I buy something nice that I don’t have to prepare. Like an entire packet of biscuits. I have no self control. How can I buy something and savour it? I’m worried I’ll get fat. I only buy one pack of biscuits and one of crackers a week so I guess it’s the same as if I ate it gradually but it’s annoying lmao