I have done this recently. Below is a pic of what I usually carry.
1. Lezyne bag with multi-tool, pouch of bits and bobs inc a puncture kit, spoke key and powerlinks, crank tool and spare plastic bit for Shimano cranks, co2 canisters.
2. Inner tube, DHB jersey bin with phone, cash and card.
3. Waterproof bag with a waterproof jacket.
I usually also have an energy bar.
1 Bottle should be fine for a couple of hours.
I can also squeeze in a battery for a helmet light too.
Hope this helps.