This came from an idea I saw on another website's thread that wasn't getting much love. When travelling, especially in hot, humid regions, you tend to sweat - especially in the back area where your daypack presses against your body.
My latest daypack goes some ways to prevent this by having another layer with a gap between the pack and the body, but it only goes so far.
As a result of all this, there can be 'an interesting aroma' emanating from your daypack. Worse if your stored food also suffers from the heat. Any solutions for dealing with this while on the go?