I tend to be something of an underbuyer (I like to think of it as being minimal) and was struck when I was at a friend's house and he pointed out that he keeps backups of his favorite toothpaste, shaving cream, mouth wash and shower gel in the cabinet under his sink. It seemed like overkill to me and I asked why he went to the trouble of having so much 'extra' stuff. (I realized that I tend to buy what I need when I've completely run out of the last bottle.) He said that he hates running out of anything and so every once in a while he just buys 2 or 3 of the things he needs.
The very next day at Trader Joe's I experimented with buying extra supplies (toilet paper, shower gel and toothpaste) and was surprised to find it felt really good to have the extras in the cupboard, that I was set for a while and wouldn't be at risk for running out. It also went against my instincts to spend money on things that weren't necessities (because, you know, I hadn't run out yet) but it actually made a difference to how I felt at home, knowing that I had plenty.
Do you keep reserves on hand of home essentials, or just buy what you need as you need it?