Green Wheelie bin... you can cut them down and they work really well. Just make sure you wash it out first, oh and don't use your neighbors one

By leaving a decent height on the sides you can carry a heap of gear in them.
The plastic is strong enough to support the weight and you can easily modify/attach some timber to provide racks/tie points ect ect.
A couple of galv knuckle joints and you can easily make up a draw bar that clamps onto the bins handle/hinge for attachment to a bike if you want to tow it.
You'll also need a length of chain and a padlock to keep it where you leave it when your on the water !
Kev