Either on the way over or way back its a good side trip south over Moose Pass to the fishing port of Seward. Great scenery and bay fishing. The upper Kenai watershed is awesom senery too. Both make the lower end look ordinary. But the fish are anything but ordinary down there. Try fishing Skelak Lake on the K. system for huge beautiful rainbows. Most of the tribs have fish in them but only a few are open such as the Russian river.
Its good to hire a guide to learn the river. But you dont need one if you have a boat or can rent one. It's fairly easy to get the hang of catching the big Kings from it. And youll have no prob seeing where the best holes are, they will be jammed with boats. Take some time to fish the other top King riv er on the pen, the Kasilof. The propriator of this site is a top guide there.
And take some time to drive out the pen to the halibut and salmon port of Homer. A half or full day out fishing for those barn doors is worth it. There are also lots of small rivers along the way with salmon coming up them from Cook Inlet. They seem to get darker quicker in those little rivers and arent as big. Check the rules to see which ones are open. I was surprised how little fishing pressure they get and they were crammed with Kings. A couple more to check out are the Anchor river and Deep creek.
Where you are going is awesom but if its your first time prepare yourself for a lot of people fishing the better places. The pen isnt wilderness Alaska fishing.