Just to echo what everybody else is saying:
This is what works for me and there is some obvious stuff, but as always take with a grain of salt:
a) Take some advil before you leave and at the next gas stop.
b) Take water with you that you can drink while you ride - either a water bottle or a camelback of some sort - i have one that i strap to the bike and run the hose to the tank bag on a retractable tether.
c)
d) hydrate a lot before you ride - your first stop should be for a bathroom on a "really" long ride, not for gas.
1. Butt soreness - having a good seat that is comfy is pretty helpful... but expensive. *Butt*, Wearing the right pants has just as big of an effect for me.
- wear some spandex bike shorts like LDComforts or just the shorts you see guys riding road bikes in (or tight fitting riding pants) that "hold your butt together"
- this makes a HUGE difference for me. When i ride in my DS pants (which are quite loose) my butt hurts way quicker than if i ride in my adventure pants (which are much tighter fitting) - the more your clothes hold your butt in place for you, the comfier it will be for the long run.
2. Back soreness - Pick 3 posture positions and switch between them regularly - 20 mile intervals. leaned forward, straight up and reclined.
-If you're taking a bag with you, strap it so it can be used as a lower back rest. (if you don't need to take a bag of gear with you - take one anyways and use it as a backrest)
My lower back is my weak point and i have to be mindful of it, so I make it a point to "stretch" while riding (side to side and front to back)
- consider bar risers that will let you relax in a more neutral position.
3. leg/knee soreness - small changes in knee angle can give good results. switch positions from/to balls of the feet, arches and heels on the pegs regularly.
- get a peg lowering kit (or lowered pegs) to increase the knee angle while riding.
4. wind noise and buffeting - this one really depends on the bike and the rider and you need to figure out what works for you and your bike.
- The Vstrom is somewhat noted as having a lot of buffeting - on that bike my solution came from moving the mirrors out about 1.5 inches, changing windshields didnt help.
-On the GSA - i cut the tabs off of the winshield adjusters so I could put it up into a higher position - close enough for me.
- wear earplugs when traveling at high speeds/long distances.
5. Throttle/hand soreness - theres nothing like a cruise control... but I don't have one on the GSA either....
- I use a kaoko throttle lock A LOT on long trips. I only tighten it lightly - down to the point where i don't actually have to apply real pressure for it to hold. This is still loose enough to make minor adjustments (without disengaging the lock) for going up and down hills and completely close the throttle quickly if needed.
Takes a quick bit of practice to get the "feel" for it.
6. Stretching -
- let a foot dangle on either side for 10 miles or so, point your toes, roll your ankles while doing it.
- Stand up A LOT: I can stand for about 20/30 minutes at a time every hour or so
- any other stretching you can think of while enroute.
7. tiredness - always try to get good rest first. Stop if you get tired.
8. Practice - repetition results in improved performance over time.