Not necessarily a prep item I bought, but I created a spreadsheet to inventory the items I have purchased. It's a way for me to track what I have purchased and expiration dates. Over the years, I have bought things and I've forgotten what stuff I've got and when. Heck, I'm not even sure where I put some stuff, so I've added a location column.
Oh man you are so right. Spent a couple of days cleaning out the garage... it was like an archeological dig. Found all kids of stuff I forgot I had. Note to self... I have ENOUGH tarps.