12th st bridge is set up for crabbin. Bridge has wide sidewalks and some people leave their pots all day and just come back and check them every so often. Thats about the only place to crab.
As for fishin, I was there all of Oct and Nov for work and SLAYED the coho!! What a blast. Missed the steelhead run. Sweet spot to catch some trout (and steel when they are in), about 7.2 miles up 26 (starting from the Bigfoot Restraunt) Its a logging road with a bridge over the river and a spot to park. Lots of different water to fish if you dont mind walking up or down river.
You can run up to Astoria to fish for springers but as far as I know none of them run up the Necanicum.
Also got a few lakes between seaside and astoria. Get yourself a "Fishing In Oregon" book. It is actually very helpful in locating fishing spots and getting there. I have an old one so info on tactics is a bit outdated but the water is always in the same spot.
Good luck......gotta share some crab if you get them. Let me know how you do. I have to go back there for work soon and if the crabbin is good I will take my pots.