Some homeowners who have placed an insurance claim for losses say that they realized something was missing months after they had filed. The inventory can actually serve as a guide to make sure you get compensated for all of your loss.
The best proof of purchase is to have a receipt for the item. The reality of the situation is that most people don't keep receipts. The next best item is to have an inventory and the more details like pictures, the better.
Contact me for a Home Inventory. Once you get it completed, put it somewhere safe so you'll have it when you need it. Saving it in the "Cloud" like Microsoft Office Live is convenient because you can acess it from any computer with Internet access.