Follow the advice of the sensible people up there about eating well for the day or so before and then having muesli, fruit, toast (my usual choice) for breakfast.
Then, during the ride, your fuelling depends on (1) how hard you expect to ride and (2) how fuel efficient your body is.
The harder you ride, the faster you use fuel, and the less able you are able to metabolise fat into glycogen at the speed of use (which is when you bonk). So, you need to nibble on bananas/energy bars/gels/flapjack (as you go along).
Try to avoid leaving big gaps between eating and then consuming too much – this will cause a blood sugar spike followed by an insulin spike, which will drop your blood sugar and slow you down.
Use an energy drink and take a swig every 15 mins. You’re bound to run out, so take some pre-measured stuff bagged up in your jersey pocket. For 180km, I’d probably start with two bottles and take another 3 – 4 bags of drink powder.
If it’s going to be hot, be careful of cramp. People seem to swear by Nuun tablets. I have some generic stuff, but (as I discovered recently) these don’t dissolve like Nuun do (hence not working).
(Of course, little of this counts if you’re only doing the 120km edition – that’s only about 70 miles which, if it’s as flat as it appears to be, won’t take longer than 4 hours..! What you gonna do with the rest of the day once you finish at noon?!!)