I've hunted deer just north of afognak on Shuyak, so its fairly similar in climate but much different in terrain. With that being said, be prepared for hard rain every single say. I'm not saying it will always rain, but it always seems to rain most days around there...
That means good rain gear, and more importantly a way to dry everything out when back at camp. Try and keep your hood on, but I know from personal experience that is easier said than done. Looking back on it now, I almost wish I would have worn some kind of a cowboy hat to keep the rain from running down your face and neck and getting your base layer soaked.
As far as protection, I personally don't think a sidearm is the best way to go... Most people couldn't hit a bear when its charging right at them... I'd go with spray, which is what I have always done personally if I'm not carrying my rifle.
In all honesty, I wouldn't go on the trip if I were you... I know I'm going against what everyone else is saying, but if I were you and you want to see that part of the world, deer hunting in the fall would be a better bet. But then your buddy might not be going then. It's a tough call, and I am biased after living in AK, so for me a tag along bear hunt isn't that appealing. For me it would be much more fun to go on my own hunt which plenty of options exist.
Feel free to message me if you have particular questions about the area, and also if you're taking a float plane up to Afognak, be prepared for a rollercoaster if you've never been in on before. My step mom only came deer hunting once after having to take a float plane up to Shuyak, couple 300' drops was all it took.... hahaha
I would be packing a side arm if it was me but not many griz in Nevada.
