On long runs (20+ miles) I use fig rolls, malt loaf, pretzels, also pumpkin seeds mixed with raisins. During recent ultras I happily scoffed cheese sandwiches, cake and crisps at the aid stations. My favorite quick energy source is Kendal mint cake, not gels.
A trick I learned recently is that if you suddenly feel low on energy, particularly on a hot day, it may be salt you need. I use Elete electrolytes in my water (no sugar, no sweetener, no flavourings - just electrolytes) and carry a 25mL bottle of the concentrate with me. I can squirt this into my mouth and follow it with some fluids and a piece of mint cake - I've found it very effective. Other people swear by S!Caps - same idea.
When I first started increasing the length of my long runs I needed more fuel by about 75 minutes. A year later, I've noticed I rarely need to eat anything on training runs of less than 2 - 2.5 hours - but when racing a marathon or ultra I go by "eat early, eat often!"
