Here are some examples of sheets that can help you manage your inventory. You can download it, use or modify according to your needs. Courtesy of Knuckle from the IPN. Go to the link below and you can found the download links there.
If you keep adding stuffs without knowing how much you've stored and suddenly too much stuffs all around, that is not prepping but that is compulsive hoarding. If you got hundreds of jars of pickles, ain't it better to trade some with other things? You can stock to many years, but if you don't have a system to manage it, in the end you'll end up storing mold and such.
This one is the sheet I use to manage inventory. It is more crude than Knuckle's but it uses different approach by using full-year view to handle stock.
The version 1.10 is already in development, trying to add some more items such as missing and trade rows, chart etc. Should be available around xmas.