On Audax rides I try to eat a little every 50km or so. I can stretch to 100km without food but not without consequences.
The 'standard' Audax distance is 200km, which is normally between 8 and 10 hours riding depending on the terrain.
If a cafe is available then beans on toast is a go to option.
If I'm riding through the night then it depends on what I can forage from petrol stations and all night food stores.
Vegetable samosas, pasta meals, falafel wraps and Pringles I find all quite palatable.
On my last 600km Audax I got a real craving for fried rice which really hit the spot a couple of times during my journey.
Plenty of fluids for hydration and coffee to fight off the drowsies is essential too.
I avoid anything overly sugary too like cake. The rollercoaster ride of sugar rush then sugar crash is not great.
The main thing is eating before you get hungry on long rides.
I discovered a few years ago that my digestive system faired much better if I avoided eating meat on rides.
I cut meat from my diet completely about 18 months ago and feel much better for it.
Other than that, regular nibbling on almonds or cashew nuts and the obligatory bananas, malt loaf and dried fruit is all good.
Post ride, there is no luxury better than a curry and a beer or two in my opinion.