To write down what I use... a lot...
While I was home for a month over Christmas we engaged in a conversation about things that we utilize on a daily basis. After having lived with a roommate that you shared everything with (except clothes, thank God, I hate sharing clothes and do not understand why girls share clothes - another blog for another time) you realize what you use and what they use. For example, we are both contact lens wearers, my brother goes through a bottle of solution in two weeks, I had a quarter of an inch left in a bottle that lasted three weeks.
Living alone you quickly realize what you cannot go without. I have learned that I drink more milk than I've ever confessed to. I eat yoghurt on a daily basis. Onions will go bad before I have a chance to use them. A large bag of chips will last me four days (read: four servings), with my brother we would eat the whole bag in an evening without any hesitation or regrets. I am surprised at the amount of mayonnaise I have gone through, mind you, I am living alone so tuna salad, egg salad, chicken salad all become a part of the regular menu. Toilet paper has become a huge dent in my wallet. I began rationing it, I had to, it was cutting in on my online shopping habits. Being in school it is expected that I will go through pens, but I have started to look for opportunities to get free swag that includes pens because I am constantly writing. I thought that pens would dry out in our house when we lived together, nope, it turns out I was actually using them for their intended purpose. I also go through a dozen eggs in a week (see above for menu). I buy tissue, I'm not sure if he does. And popcorn, I have gone through probably 100 000 kernels since living on my own.
Things that I have not bought since living on my own: trail mix, strawberry jam, doritos, coffee (I am a tea drinker) and all of the stuff that goes with coffee, broccoli soup, those sponges that have a liquid soap tube as the handle for doing dishes, and I am certain there are more things but it is interesting to see what you ascribe to as your habits until you have engaged in the study of self.