Fenders, of course. Long as you can get. That merino wool base layer makes all the difference: If you do get wet, you still don't feel cold. I use them even in the summer if I know I'm going to get wet. I'd rather have the wool than a shell. Wool T-shirt and a windbreaker with the pit zips open, nylon pants for light misting and cover them with some gore-tex-ish pants when it's serious. You're throwing off enough heat that you cook off anything that gets through and keeping from sweating is a bigger issue. I like a hat with a big enough stiff brim to keep the rain off my face, though a helmet visor would probably work. On a typical ride of less than an hour I find thick merino socks with sandals are still plenty warm even with near-freezing rain, and for longer/colder rides the socks hold any toes that freeze off so I don't have to retrace my route looking for them.