I've said this before and I'll say it again here. Disney, DCL - and other resorts with this problem - need a token system. Every hour have someone walk around and put tokens on unoccupied chairs with stuff. Every hour the token is a different color and says "return this token so we know you are using this chair" Install a few token boxes for returning tokens. If the token is still there in an hour when new tokens are dropped, the stuff goes into lost and found. Just like when the meter maid (boy is that an old fashioned sexist term) chalks your tire in the one hour parking zone.