I spent a couple weeks backpacking in the national park a few years ago, no trails there, didn't go in the state park but it must be similar. You should expect to be woken up by giant animals outside your tent almost every night, if you're sleeping in a tent. You should expect mosquitos and swamps which really aren't that bad but sometimes you'll walk into an area where you can't get your pack off fast enough to get the bug net out. The other thing that suprised me up there was how big everything is and the obstacles you'll run into just trying to get from a to b. Maybe that won't be such a problem where you actually have trails, but icy river crossings, deep alder swamps, cliffs, grizzlies in your path, and just the fact that everything looks a lot closer than it is made for long days, extra long beacuse you can still be hiking at 11pm. I'd bring a pair of those knee high rubber boots. It will be a good time, eventually you can just go back to sleep when there is something large outside the tent.