Hi Paul,
Late to the party here, but I may be able to contribute some thoughts...
All of my solo 400km rides are completed within 24 hours and so this means depending on season there is more or less dark (really dark and for a long time if it is a moonless night in, say, October). Temperature and weather over the whole of the route needs to be considered and as most of mine involve going from the valley where I live up to and over mountain passes; there can be a chance of really cold nighttime temps and even the possibility of snow or freezing rain "up top" even when it is sunny and mild below. I try to equip the bike and pack for it accordingly. Also...! I try to squeeze in between 30min and 3 hours' sleep when I can depending on my running average for that 24-hour window. A lot depends on terrain and weather conditions. My last included 91kms of 5% upgrade followed by 14kms of 8% climbing before a blistering downhill timed for the dead of night as it happened. I've gone straight through without sleep but feel less hammered by the effort when I can engineer some rest breaks, so sometimes that means tossing in a lightweight self-inflating mattress and a mylar sleep-sack or looking for some hay bales to lay on at road-maintenance sites. For me, the benefits outweigh the extra weight but this is something that varies with the individual and for me, over time (i.e. I got older).
For lighting, I prefer dynamo-based as my primary lighting source with battery backup for those occasions when I simply need more light. I came whooping 'round a corner to belatedly find a rockslide in my path one time. "Belatedly" because my first notice of it was when the bike jumped and I nicked three teeth off my large chainring before going down. Of course, this stopped my forward movement and along with it, my dyno-generated lighting so the fall to the pavement was in stygian darkness and seemed to take forever before the inevitable "Ouch!". I learned that night to always start the battery lights before the sketchier sections in case my speed (suddenly) dropped too low for "bright enough" dyno lighting to see such things in advance. I used a strap-on battery pack (which I occasionally carried in a jersey pocket) and two battery lights clamped to the tops of my drop handlebars, my HB bag sitting below bar-top level thanks to a T-bar. It worked well enough for the distance-aiming I wanted for those lights and where oncoming traffic was not a consideration.
For tires, I prefer 38mm road tires if the bike and mudguards will accept them with adequate clearance. Otherwise, my narrowest preferred fallback is 32-35mm, again depending on clearance, with pressures adjusted for 15% drop under load of bike and rider. I tend to feel too much road shock and cumulative fatigue doing those same rides on 28mm tires.
Saddlebag: All my rando bikes are equipped with a rear rack and so it has worked well for me to use an expandable rack-top pack. Mine are made of Cordura nylon, have side pockets and a top that accordions upward when needed for more space.
One thing that positively transformed long-distance riding for me is the suspension seatpost. I have fitted Thudbuster ST (Short Travel) sus-posts to all my rando bikes. They don't absorb nearly the shocks my LT (Long Travel) Thudbusters do, but they surely take the "edge" off chip-seal and pavement irregularities and these were taking a greater toll on my overall endurance than I thought simply by causing more fatigue due to cumulative road shock over 24 hours' riding. Fitting tires with a larger cross-section/volume could accomplish the same end goal, but clearance quickly becomes an issue on most 700C-wheeled road bikes used for rando work. 650B opens up a lot of possibilities here because the frames are generally built with wider clearances for fatter tires fitted with mudguards. I am seriously considering using my Enduro-Allroad bike for next summer's rides as it has 26x2.0 tires and a TB LT seatpost and isn't really any slower in practice than my more rando-focused road bikes.
I generally carry food I can eat on the bike while underway and try to regulate my water intake to minimize toilet stops. Even so, like with the sleep breaks, I have taken to adding food/get off and walk-around breaks as I have grown older (63 in March) and still manage to get in under my 24-hour deadline so I'm guessing the rest and breaks haven't affected my Average Overall so much after all and likely boosted my Running Average to compensate. Running average tends to be above 25kmh, so about 23.2hours of actual riding time for 400km/248mi at that pace.
My preference is only for steel bikes and I have done enough warranty consulting for local bike shops in the past to shy away from using carbon forks myself. Sometimes my routes include gravel and it is amazing the damage a thrown rock while underway can do to a carbon fork (not to mention myriad other causes of damage, most of which appear totally innocent at the time but result in Real Problems when examined more closely). My steel rando bikes are essentially road-touring bikes, all weighing around 14.5-15kg dry and fully equipped. All have derailleur drivetrains and I usually remove the front racks for rando rides except for those occasions when two small panniers are my carry-bags for the ride. When I have done that, I sorely missed my HB bag, so it is back to the HB bag and rack-top pack combo for me.
As for what I carry...well, it is only for 24 hours (I tend to top out there, finding it less fun to go further in one go), so I carry things like energy bars I can eat while riding, dried bananas and fruit, beef or turkey jerky, and so on. I have taken a small homemade spirit stove and cup set (pictured below) for brewing hot tea or warming dehydrated soup or even my "ultralight touring setup" if I plan to do back-to-back days of, say, 300kms each. See...
http://thorncyclesforum.co.uk/index.php?topic=12866.msg97165#msg97165 That has everything I could possibly need.
For one and don rides, I make sure my bikes start in good shape (as they always are) and then take only a spare tube, instant and vulcanizing patch kits, a spare mini-pump, tire levers, and a multitool for tools. For clothing, I generally take a longsleeve wool jersey sometimes with nylon wind-facing on the front, a wind jacket, and tights or wool arm and leg warmers, something to keep my knees warm as the temps drop with nighttime and altitude (the two usually correlate given my routes and location). Rain gear, of course: Rain jacket, helmet cover, rain pants, booties, gloves which can doube in purpose to add warmth if needed. Almost never carried in the summer months, almost always at every other time of year.
As usual for me, water is an issue and the mountain roads I ride are often alongside rivers and creeks that are inaccessible due to the way the banks are configured next to the road or because they are far below road grade. As a result, I always carry at least 3l with me and still sometimes toss in my SteriPen in case I can find a source. There really aren't stores and such where I can refill for the criticl middle part of my long rides, so this is just something I have to consider and carry to address. Those 3l amount to 3kg in water weight plus containers and holders, so that adds almost as much to my bike weight as everything else I usually carry.
Hope something in the above may prove useful to you, Paul. All support and continued encouragement on your efforts.
Best, Dan.
