At the 16/20 NAs in Alameda a boat almost flipped and the crew fell overboard. The skipper was tangled up in the main sheet and sheeted in probably sailing 10 knots or so. Completely wrapped up and unable to do anything but steer the boat with his wrist.
We came along side in the SC Skiff and I had my knife at the ready to start cutting the entire mess apart, especially if the boat flipped. Luckily, I was able to uncleat the jib, slow the boat, and untangle him without too much trouble. A knife is an important tool aboard a sailboat.
At the Extreme 40 Sailing series in Boston 2 weeks ago, I noticed that they had a knife strapped to the trampoline on all four corners. It's actually in their class rules to have knives onboard. It's a crew member's job everyday prior to racing to make sure that the knives are sharpened and ready for the day.
Here's a pic that I snapped from ETNZ, see the knife on the tramp in the foreground?