Thanks, everyone, for all the good comments.

@rstine: Oh, a month's soup is only the beginning. See Myscha's excellent Bulk buying 101 for a few more ideas.

@Kevin: Yeah, that's my main point--analyzing these things as investments isn't the usual way to look at it, but I find it useful to think about it that way.

@Hilary: Right. The decision to change to cheaper products is completely independent of the decision to stockpile them, and the fact that some products are much cheaper in bulk than others makes it easy to confuse these issues.

@Debbie M: Yes, all the time and money that you invest in taking care of yourself and your stuff can be treated as an investment as well, and it's interesting to crank the numbers and see where these things make for superior investments. On the other hand, you can take it too far. For example, you could probably make a financial case against brushing your teeth--an hour a week spent on oral hygine that could be spent earning money--but having healthy teeth has huge non-financial payoffs that swamp the financial ones.