Mobile phone with a fully charged battery (and spares if possible).
Waterproof full body cover (taped seams)
map (OL17, OS Landranger 115 or Harvey's Snowdonia North)
first aid kit
emergency foil blanket or bivi bag
emergency vegan food
spare warm clothes in bags for rest stops (optional)
head torch with new batteries.
Please test all your kit before you race.