I realize you already made your trip, but I will answer your question anyhow. These tips are not regionally constrained to the Olympic Peninsula.
When setting out to wet places or in rainy weather always take a second pair of boots. In my experience from the army every shoe will let in water sooner or later under heavy rain. Always pack a couple of durable plastic bags with two heavy duty rubber bands (useful for other tasks as well). So if you have to cross a stream you just step in the bags and seal them off over your calves with the rubber. They will get you through wider streams than you'd think.
Keep in mind: improvise - adapt - overcome. Always bring your wits when you go hiking.
Change your socks often.
Clothing is very individual, and everyone finds out what becomes him most. However I am of the opinion to dress light. You should be cold before you walk. If your still cold after the first mile, walk faster! You cannot avoid perspiration, but try to limit it. Soaked feet will not be a problem for 3 days and 30 miles, but better learn good habits early. Use synthetic material that can dry fast. Get some nice comfortable cotton clothes for the evening/night, but make sure they stay dry. Do not wear them while sleeping, even without a tent perspiration during the night in the enclosed sleeping bag will make them humid. Also, sleeping bags warm better through direct contact to the skin.
Use compression bags to pack your clothes. You save space and will be able to pack a sturdier pack and well-distribute weight. This makes a hug difference the heavier your pack gets. I assume you know this, but just to be complete on these essentials: Carry the weight on your hips, not your shoulders! The hip belt and frame are the most important features of a pack. Consider buying a Camelback (cannot post more than 2 links sorry). Having the water easily accessible through the hose will encourage you to drink. It's easy to forget drinking in cold weather, but it is very unpleasant later on and can get dangerous sooner than you might expect.
4) Sleeping Another useful tip in cold and wet weather, assuming your a purist and not sleeping with a closed tent, is to put your walking clothes that are humid between the inner and the outter layer of the sleeping bag: The heat from the inside will dry them through the night (just remember to let the outer cover rather loose so the hot and humid air can escape.
With a closed tent you can use a one layer sleeping bag and hang the clothes in the tent (but leave it open so warm and humid air gets out).
Buy a Jetboil. In a less than two minutes you can fill a bottle with hot water. By holding this to your chest and belly you will fall asleep easily even in extremely cold weather. Before you drift off throw the bottle to the bottom of the bag, warm feet are a luxurious pleasure when sleeping in cold weather.
Might seem ridiculous to mention, but you never know who might read this: before Hiking anywhere, especially alone, be sure of your navigating skills! Always bring a compass and a map. I understand we have access to GPS and iPhones and whatnot - but I know just as well that whatever can go wrong eventually goes wrong. It is Murphy's Law. Google it. A compass and a map doesn't go wrong, as well as informing someone of your approximate locations and est. return date. Trust in the most simple solutions.. it should be at least your plan B.