I also find thing I've bought and don't remember. Leaving tags on is a good idea. Last time I was manic I bought two large flat screens, apparently I didn't like the first one so I bought a second, in cash. I normally don't make even small purchases without careful consideration. Luckily I was able to return the tv.

I too get obsessed with certain things, and feel the need to collect every single item I come across. But when I come down, these are usually things I don't need, will not use, or don't like. I'm on a very tight budget and thank god I don't have credit cards, but I still manage to cause financial hardship while manic. Since I don't drink or anything of that nature, the shopping has to be one of the most damaging symptoms for me. It's like an obsessive compulsion that just takes over, when "normal" me is pretty frugal.