Just a few comments:
Since, it is a car-camping place you COULD definitely take more luxuries. However, I totally understand you wanting to try out some UL gear and techniques. It is actually a pretty good opportunity to go light without risking your safety. The first aid cabin is never far away :P
I assume the Camelback Viper is for day hikes and such. If you already are bringing the daypack, what are you going to use the Ion for? I find it easier at Boy Scout camp to just pack everything up in duffels (which you already have in your list) and just bring a daypack for carrying stuff around camp and on day hikes.
You might want to bring a watch. At my council's scout camp in the Adirondacks (it's called Sabattis), there is a schedule of activities/classes and a watch is very necessary.
I don't know how cold it gets at night in Idaho but I would probably recommend a jacket of some sort, whether it be fleece, synthetic, or down. For a car-camping place, I would think a cheap fleece jacket would be the best choice since weight isn't critical.
Also, I don't know how hot is gets, but a pair of shorts might be nice? I guess I'm biased because I LOVE shorts.
At Camp Easton, do you have a dining hall or do you cook your own food? If you have to cook your own, you might need utensils and a bowl/plate?
Finally, don't forget to bring a water bottle of some kind.
Overall, looks like a pretty good list. Good luck and have fun!