I just remember everything.
I do have a great memory though, so that makes it easy.
I do have a list of all my products though, I add to it each time I get something new then email it to mum, my sister and my fiancee, so that when they buy me gifts they wont get duplicates (Im hard to buy for because the only things I really like a clothes, shoes and cosmetics, so its easier for everyone if they buy me MAC )