Packing your bike up correctly, so that you can get to the things that you will regularly need during your trip, without having to unload the bulky items is essential.
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. It could be as simple as a woolly hat stuffed in the top of a (waterproof) bag. If space isn’t so tight, you could stash a pair of slippers and a jumper in that bag to help you to warm up after a long day in the saddle.
Surviving big mileage trips is about managing morale. Just because you have spent six months planning this trip doesn’t guarantee a good time from start to finish.
Keep morale up while you are riding by keeping 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. You can party hard, just not the night before a long riding day.