For those of you that have nailed your staples and really only buy what you need, when you go shopping do you buy enough to last a certain amount of time? Like if you want it last a few months how much do you pick up. (I know answers will vary due to length and specific regimens but I am curious) If not and you only purchase one bottle/jar/tube at a time. Then how long does it take until you have to repurchase? I hope my question makes sense.