If there was one thing I learned on my weight loss journey it was too look to see how much was an actual serving before putting food in my mouth. I used to guess what they were, but you really need to measure and weigh, so you know what you are getting yourself into. I have a food scale and I have several sets of measuring cups and spoons
I remember the shocking day when I was making my son a peanut butter and jelly sandwich. I would always get a spoon and have some peanut butter when I was done making his lunch. One day, I actually looked and found out that I was eating more than a tablespoon of peanut butter which was more than 100 calories mindlessly! That is a lot of calories!
If you can't trust yourself or need to grab something easy for a snack, grab some that are already portioned. I get hungry sometimes in between lunch and dinner and I know I always have preportioned servings of some kind of nut butter in my pantry. Just grab one of those and an apple or some celery. Easy Peasy, right?