This is a . . . really fun thread! Some random thoughts.
Why ride long distances? Why jump out of an airplane; climb 1,000 feet of shear cliff without a safety line, participate in a triathlon, drive fast cars around a race track, swim across the English Channel, sail single handed across an ocean . . . ? Just because you want to. What more reason do you need than that.
Helmets? Modular or non-modular is not as important as fit. Different brands, different models fit different heads. Some heads are round, most are not. Lots of advantages for modulars riding long distance as noted previously by others, but . . . be sure what you're wearing fits your head shape.
Can't ride 700 miles in a car? Me neither, but I can ride 1,500 miles on a bike. On the bike I have good posture because the bike has been modified with risers and a better seat (custom Sergeants) that allows me to sit upright, weight evenly distributed along my spine to include the added weight of my helmet. I have yet to own a car with seats that allow proper body alignment. Even with lumbar adjustments, they're still torture racks over a long haul.
Carry tools in your tank bag? Really? If you're horse requires that kind of attention, you need . . . a different horse. For me: right bike pannier has everything I'm carrying along to support the bike; left bike pannier carries clothing and everything I need to support me when I make an extended rest stop (hotel); top box carries what I might need along the way like heated gear, flashlight, extra gloves, odds and ends, laptop (the only place it safely fits); and my tank bag has what I might need more quickly during the ride, pen/paper, trip notes, sunglasses, extra pair of gloves, cleaning cloths for my glasses/helmet and snacks.
Distance riding tip: carry some Red Hots (or something like them) and some sweet or sour hard candies in your tank bag. When you start feeling tired, excite your taste buds (stimulate your brain) with something attention getting and you'll perk back up for another 30-60 minutes.
Earplugs? Absolutely essential. In helmet speakers don't work well for me, still to much road and wind noise to contend with. I rely on in-ear custom fitted stereo ear plugs that plug into my Sena 20s. Much MUCH quieter and fatiguing. On long highway stretches I listen to music, stories or briefly catch up on the news (XM Radio), but when in city traffic, carving the curves . . . silence rules - no distractions from the task at hand as I smile away every mile.
Physical conditioning? For a single day distance ride; 1,000 or more miles, it doesn't make a lot of difference. Just go for it and you'll know when to quit. For multi-day long distances, think Iron Butt Rally where you might be riding 1,000 miles/day for 11 days . . . yeah, you need some preparation. Before my 1st IBR ride, I sought advice/assistance from physical therapists, a nutritionist, and a sleep specialist as well as my doctors (I'm old enough to have many friend all named "Doc").
Getting sleepy? This is a serous topic for long distance riding. Like Uncle Phil noted, if you feel your eyes wanting to blink shut "just for a second or two", DO SOMETHING. Initially, I'll go to my red hots and hard candy to perk back up and make a few more miles to a good place to pull in and take a break or check in for the night. More dangerous than the nodding most of us are familiar with from our school days are micro-sleeps.
Micro-sleeps? Even more dangerous are "micro-sleeps" where your eyelids aren't feeling like they need a "short" rest; you're feeling fine, or so you think. Your brain adjusts to a lack of sleep by closing down the portions you're not using as you ride along a monotonous stretch of your ride. Your brain will keep you on the road, making the gentle turns but you'll basically not be aware. My example is being half way around an off-ramp and not knowing how I got on it from the interstate I had been riding on. After stopping I determined I had passed my intended exit several miles back down the road, completely unaware.
Best indicator you need to stop is when you find yourself unable to maintain a constant speed. You realize you're going slower than you want and accelerate back up to your cruising speed only to find that shortly after you're doing it again, and again . . . Time to STOP and get off the bike. A former Navy Surgeon General, also an IBA rider, published an excellent paper on this. If interested, let me know and I'll try to find it and send a copy.
Riding 1,000 miles in 24 hours or less seems impossible until you do it. Then you'll wonder what all the fuss was about.
Shuey
IBA 423