Travelling as light as possible is fastest. However, travelling light can also be very dangerous. It’s your decision as to what risks you’re prepared to take.
This is largely a matter of preference, but try to eat and drink regularly.
You are likely to become dehydrated during this walk. I would recommend that in addition to water, you take some form of isotonic drink eg. Lucozade Sport (not Lucozade Energy, which will dehydrate you further) or isotonic Isostar. Fluid from an isotonic drink is much more readily taken up by the body.
Salty food, eg. ready salted crisps, can also help rehydration if accompanied by a drink.