carry an 18 inch length of thin flexible plastic pipe so you can fill your bidon from those taps in garage loos that sit over tiny sinks, too small to get the bidon under to get water in it.
oh - and on a 300k such as the Invicta 300 last weekend, remember to bring tyre levers. And more than one inner tube. So if, like one rider, you have two punctures, you are not completely stuffed. And a small headtorch on the helmet, so if you have a puncture in the dark and fix it, you don't forget your pump, and leave it by the road in the middle of nowhere.
These are true tales. Strange, but true.............