Furthest I ever cycled in one day was 140 miles (Sittingbourne to Leicester) on a camping trip, it was a beautiful summers day with a slight following breeze and I could have gone on forever.
The trick is to
never never never cycle up hills but to get off and push your bike up them.
Also, try not to have a fixed destination or you'll spend the day fretting about whether you're going to get there before night and will tend to push yourself too much.
Personally I just kept on going til dusk, then pulled off the road and set up my tent in a wood wherever I happened to be..
Another trick is to
eat at the very first sign of feeling hungry, you can either munch as you pedal along, or even better
stop and eat while propped up against a farm gate.
I once learnt that the hard way in my early cycle-camping days after about 50 miles when I began feeling peckish but I thought
"i'll do a few more miles before stopping to eat".
Big mistake! As I pedalled along I began feeling faint with a hissing in my ears, dim vision, spots before the eyes, cold sweat, and my stomach was screaming out for food, so I staggered onto the grass verge and ate like a horse, ravenously devouring food and drink from my rucksack and was right as rain after 15 minutes.
I later found out it was something to do with low blood sugar levels and cyclists even had a name for it- "Hunger Knock" or "The Bonk"..
That's why racers avoid it by having small bags (musettes) of food and drink handed to them at 'feeding stations' during races to munch while pedalling-
