Before racing/exercise apply GurneyGoo™ liberally to areas prone to friction eg toes, crotch, nipples, feet, armpits, shoulders in vicinity of pack straps.
For the best protection, rub in a moderate amount 12 hours before start in addition to the liberal layer at the start.
To prevent hand blisters during long kayaking sessions: thoroughly rub GurneyGoo™ into hands up to 8 hours before start (eg night before), and no closer than 1 hour before the start of your race.
For some of us, a shower on waking on race morning is a nice way to wake up, warm up, and soothe any pre-race nerves. If you've applied GurneyGoo the night before (a great idea for maximum chaffing prevention), then a light shower won't remove the all important component of the "night -before" GurneyGoo.
The all important bit is that some GurneyGoo will remain, having had your sleep time to "soak in" to the outer layers of epidermis. A light rinse in the shower won't wash this off much at all. If you scrub with soap and flannel and hot water, then yes you'll remove 90% of this, so avoid scrubbing and keep the shower short.
So, a shower is all good so long as you don't scrub the bits you've applied the GurneyGoo to.
After your shower, give your bits a second application of Gurney Goo and you're all set to go!
The only exception is kayaking fingers if it's less than 2 hours before the event, in which case, make sure your shower is more than 2 hours before and apply Goo sparingly, and vigorously rub your hands together to heat and absorb.
If it's a long and chaffing-prone event, then you might also consider applying some goo to the clothing that can cause chaffing in addition to your skin. eg cycle chamois, running short crotch, sox, bra strap, kayak pants, etc.