In reply to BarrySW19:
Take full waterproofs (top and bottom)
Layering is the key - the weather can change during the day.
Quick drying and stretchy, so things that you might already have, like tracksuit bottoms are fine.
Check the weather - if hot take:
sun cream, midge cream
It can be quite a bit colder in the wind, so a windproof layer is useful (can just be your waterproof)
trousers with zip off bottoms so they convert into shorts give quite a lot of flexibility.
Jeans are pretty slow to dry if they get wet, but seem to be the latest trendy thing - I think you can get quick drying, stretchy jeans these days, but they cost a bit...
Make sure you take plenty of water and some sarnies, a nut key, helmet,