I’ve done it twice and both times with a small pack. No risk of bottle loss (there are plenty scattered around so it happens) and easier to carry. I just put 1 – 1.5L of water in depending on weather. Mine leaves access to pockets for food and has enough space for tubes, tool etc. so that the bike is light and easier to carry.
Never understood the land cruiser thing. They seem really heavy. I just ran my standard intermediate tyres (Vittoria XG pro) and pumped them up hard (65 ish). If you are light, ride with a bit of sense and don’t crash into the water drains you should avoid punctures. The majority of punctures I saw were people coming down the slabs and pinching. I don’t see there being much time to make up on the descent*. Big gains to be make if you can get a group at 20+ mph on the road and march up the climbs.
*ride or run it is up to you. Personally my aim is to get round as fast as possible so I’ll decide on the day. Same as in a normal race – if it is faster to run, then shoulder and get on with it.