Although I am already questioning some of the things that I have packed in my rucksack (will I really need a sleeping bag that is comfortable to -5 degrees C?), and also already picked up on a few luggage oversights (a travel sink-plug and suntan lotion that actually works being two), I can happily report that I have already had to make use of both my sewing kit and first aid kit.
Needing to perform some open-toe surgery on a painful blister, the sewing kit provided the safety pin to burst the blister, and the first aid kit provided the antiseptic cream and elastoplast. No needle and thread was needed to stich up my big toe after this delicate and complex operation.