Too many to mention. I do this trip regularly. Not too many skateparks on the very N Cal coast but camping in the Redwoods is amazing. Then move north to Brookings/Gold Beach/ Port Orford (camp at Humbug Mountain or Cape Blanco both super nice sights right on the beach). Next up would be Coos Bay for skatepark (camp at Bastendorf). Then comes, Reedsport, Florence, Waldport, Newport, Toledo, Lincoln City, Bay City, Nehalem Ramp, Cannon Beach, Seaside and finally Astoria.
Lincoln City is the highlight of the trip skate wise. You could skate there for days and not get bored. Bay City is an empty little gem that no one ever goes to or really knows about and there is a county camp site right next to it. Bear in mind that some of the older parks like Newport, OG LC and Astoria are now quite rough due to the weather. I lost some skin yesterday due to a coastal park.
Hikes: Humbug Mountain is the highest coastal mountain that comes right out of the sea. Salmon River Mouth. Cape Lookout. Indian Beach to Seaside are some of my favorites.
You can often camp on the beach. Its legal as long as its outside of city limits and there are no signs but you can even get away with it when you are in city limits, just be discrete.
Weather during Spring break can still be terrible but so far the Oregon coast hasn't really had a winter, so who knows.... generally speaking the further north you go the worse the weather could be. Pay attention to NOAA. Brookings and PO are considered the 'banana belt.'