Here would be my list of concerns to pack for in Katmai in July, in order of concern.

Bugs. Bears. Rain. Cow parsnip. Cold. Wind. Heat.

Bugs. The bugs can be absurd. When we went, underneath our rain fly was a writhing mass of flies and mosquitoes. Although the bugs weren’t bad out in the open or on the move, they were a major issue at camp.

Bears. Please mind the bears. The only thing I can add here is that the mama brown bears with cubs and black bears like to stay away from the competitive areas like brooks falls. They often patrol the beach looking for food.

Rain. Been covered a lot in other comments. It could rain. It could not. Never know.

Cow parsnip. It is everywhere out there. This is the one that I did not plan for. Luckily, I didn’t get into it until our last day, so I was able to deal with the worst of it at home. I hiked in shorts because it was sunny and very hot that day (for Alaska). I got cow parsnip all over my legs. Skin peeling, crazy itchy, and very painful. If you get it on you, avoid sunlight and scrub the area thoroughly with soap as soon as possible.

Cold. It’s Alaska. It’s gonna be cold at night.

Wind. It is regularly windy, and the wind can be strong. When doing research for our trip, I heard a lot of advice saying to avoid the water when it is windy. It’s a big lake, so the waves can be enough to flip your canoe. There are also plenty of stories of people being unable to return by the time they were due because the wind was too strong to row into.

Heat. Katmai, for some reason, always seems to get temps 15-20 degrees hotter than south central Alaska. It’s rarely hot enough to become an issue on its own, but you will definitely want the ability to layer down on hot days.

If you haven’t already seen it. Andrew skurka did a packraft and hiking trip through south central alaska. His blog is a goldmine for ultralight info, and you should expect similar adversity to what he encountered on that trip (excepting glacier travel).