You want to be on the West side of the Necanicum. There is no way to cross the river if you park behind the high school...And bring a shrimp pump. Fish the channel when the tide is almost out. There is also a sea run cut-throat run that shows up soon. I don't know if the ''cuts'' are legal in that river. They used to be caught along the Par-tee golf course, but I heard the fishers have been run off years ago.
Then there are always surf perch! Don't stand in one place, follow the school with live bait and light tackle.
....One more place in Seaside that most of the locals don't even know about (check it out on Google Maps). It's the old millpond behind Less Schwab. There is easy and legal access and a path that goes around the pond.
Don't tell anyone!