If you've got up to 70 miles over similar terrain then you shouldn't find it too difficult to do another 30. 8 or 9 hours sounds realistic, set off nice and slowly and you should still have some energy at the end.
My approach to longer rides is to eat a big carb meal the night before, and then maybe a big portion of porridge or oat cereal for breakfast. Don't eat too much just before you set off, if you're too full your body willl concentrate on digesting rather than powering your legs.
Water is good, but a bottle of Lucozade/Gatorade will also give you a boost - drink and eat little and often - drink before you feel thirsty, and snack before you feel hungry.
Gels have their place and aren't just for racers - they are handy on the bike if you don't want to get off and stop - but personally I think gels taste grim. Some people find gels and certain sport drinks give them an upset stomach - if you've done ok up to now probably best to avoid them until you know if you're one of them!
Cereal bars, flapjacks and bananas are good to snack on, and Lucozade tablets are also a good top-up. As Gerry Attrick says, if there are cafes etc on the way, stop and have a sandwich/piece of pizza etc. If there aren't cafes, a few sandwiches or pieces of cold pizza might also be good to take along so you're getting some salt and carbs on the way.
As for afterwards, something high in protein will help your muscles to recover - but basically whatever you fancy, curry or steak and chips
Apparently marzipan is a good recovery snack as it's high in protein.
On my first 100+ miler I stopped every 20 miles for a snack, a stretch and to get the circulation in my bum moving and it seemed to work out ok...
Don't forget to stretch properly afterwards and good luck, hopefully it will be the first of many more rides.
