When I go windsurfing I always bring a few tools. Screwdrivers to attach fins, a pair of pliers to untangle lines or knots that have been pulled really tight (great when fingers are frozen!). And a knife to cut lines.
This tool has it all. On longer windsurftrips the extra features come in handy to open cans, bottles and so forth.
Leatherman has pricier versions but I found the extra's on them not benefitting for my windsurftrips. Check for more details on Amazon.