small day backpack.

rain jacket – it can be just a ‘shell’ but it must be seam-seeled waterproof.
merino or thermal long sleeve top
extra fleece/mid wieght wool top we have just added this to the list.

long tights or trousers
warm cap or beanie
polyprop gloves
survival blanket
own snacks, gels, energy bars etc
water bottles/bladders – enough to carry 2 litres of water at all times
headlight for night-time with back up battery
reflector stripes or vest or back flashing light for night-time running

Good to have
cell phone (recommended but optional)
gps/compass – optional
running gaiters

Good to leave at TW bag drop (just in case)
Extra pair(s) of dry socks
Water proof over trousers
Extra warm top…
Spare batteries for headlight