From watching gcn videos I had the impression that when cycling you needed to eat foods that have a high sugar content as they all seemed to survive on energy gels, cereal bars, coffee and cake. If I am cycling in the middle of nowhere and there are no shops what do I bring with me from home?
No no no.....
GCN - well, whilst entertaining, they do talk some crap. You need complex carbs, not sugary stuff. Energy gels are for emergencies.
Drink, can be water, water and a fruit juice added, or a carb drink (long distances). Food, just take something you can eat - bananas, cereal bar, sandwich cut into bike sizes.
If you are thinking about caffeen and sugar, then no wonder your HR is spiking. Eat normally. You don't need a whole load of food on 100km.
I do a fair amount of MTB'ing in the real middle of no-where and I'll have a couple of gels and cereal bars as an emergency back up. I'll carry a couple of bananas and fluids of a 3-4 hour ride. The last one I did a few weeks ago, I just had fluids over 3-4 hours, and a pint and a bag of crisps near the end of the ride.