Packing your bike up correctly so that you can get to the things you’ll regularly need during a trip without having to unload bulky items is important.
You don’t want to be unpacking a week’s worth of clothes at the side of the road in the rain while you look for your waterproof trousers. Even if you’re packing light, it is important to take something comfortable for when you have finished riding for the day.
It could be as simple as a woolly hat stuffed in the top of a (waterproof) bag if space isn’t so tight it could be a pair pf slippers and a jumper to help you warm up after a long day in the saddle.
Surviving big mileage trips is abou managing morale. Just because you’ve spent six months planning this trip doesn’t guarantee a good time from start to finish. Keep morale up while you’re riding by being as comfortable as possible and keeping a handle on directions and where you plan to stop.
Maintain morale off the bike by eating regularly, not starting a full day’s ride with a hangover and by getting the best night’s sleep as possible. Even if you are under a tarp laying next to your bike, as long as you are warm, dry and well fed, you should have an amazing experience.