Two bottles, about 1.5 litres so thirty miles should be ok.
Will buy the map as it will go in the back pocket. Small saddle bag with couple if tubes and patches in case tubeless comes a cropper.
Maybe a dozen gels, some bars and something salty when I overdo the sweet stuff.
Have done similar distance before but slightly less elevation as part of a group. Hopefully going solo should speed things along.
Do people doing it in the height of summer take proper lights or just a small helmet mount in case it goes horribly wrong.
Will be getting into Winchester 7.30 ish so even if it takes 14 hours I should still be done before “proper” nightfall