Waterproof boots, with a good sole and ankle support. This should not be the first time you have worn them !, a good way to avoid blisters is to wear two pairs of socks. A thin pair next to the skin and a thicker pair over the top.
Waterproof jacket, not just shower proof, preferably with a hood.
Waterproof over trousers.
Warm clothing not jeans, something like warm track suit bottoms are OK, remember several layers are warmer than one thick one and gives you the versatility to remove or add clothing as necessary.
Woolly hat and gloves.
Torch, with spare batteries and bulb.
Small first aid kit, e.g. plasters for blisters etc.
Map and compass.
Bivi bag, orange large heavy gauge plastic bag basically, available from most camping shops.
Food for the day.
Emergency rations e.g. chocolate bars .
Flask, unbreakable ideally.
Rucksack to put it all in.
Finally, it is often a good idea to have a change of clothes in the boot of your car in case you do get wet. Together with a second flask, for a hot drink at the end of the walk.