What was the silliest thing you've ever bought? How do you stop yourself from making unnecessary purchases?

Here's mine: I bought a camera lens last year that I still haven't used. And recently I bought a cowboy hat!

I think the silliest thing I have ever bought is suspenders and glasses. My best friend found out she had to start wearing glasses and she was feeling, in her words, "geeky". To help her feel better, I bought a pair of non-prescription glasses (that looked almost exactly like hers) and suspenders so she wouldn't feel so out of place. She thought it was extremely cute and funny.
The way I stop myself from making unnecessary purchases is I think long and hard about how often I will wear or use the purchased item or I wait a month or two before buying it. Sometimes I think it is good to buy something unnecessary (but cheap) from time to time.