Brag mat...
Its just a mat in centimetre increments usually from 110 to 130cm long that you can lay the fish on for measuring. Then you can brag about it later.
Its handy to take a photo of the fish while its on the brag mat so that you can back up your bragging rights - if the catch is braggable that is.
The mats also roll up, they don't take up too much space and are fairly light.
Campbells Pro Tackle online site have the Shimano ones for $14.95 although you can get other more expensive versions.