Hi Allen
Depends on a few thing, such as what where and when.
If in the UK, then the weather can be just as cold in August as it is in March, so generaly and An Du Ru Fox mentions, normally same clothes as all year but less layers.
Stalking: If you are doing traditional stalking, i.e crawling, lying down, etc then you can get away with a heavy cotton duck trouser, but if the ground is wet then it would be better to have Loden.
Loden is a very densly woven wool cloth, which has been boiled, so the it is almost indestructable and pretty much waterproof, although there are no membranes in Loden. It is also extremely breathable. Loden is very expensive though as it uses a great deal of skill in its products and not that much is made.
If you could expand a bit on what, where and how, we should be able to give you some more constructive advise
Andrew
Rugged & Tough
Carhartt, Blaklader, Harkila, Seeland, Workwear & Country Store