Having clothes for all types of weather will be a must, Rhino. Eagle Lakes seems to be due west ( 400 miles) of where I live in Ohio and we never know what the weather will be like in 5 minutes! Seems to be the only thing I can say for Ohio weather is that it will be windy at the very least. I imagine that IL will be similar to Ohio, weather wise.
Good idea on the umbrella, might have forgotten that one, it's now on THE LIST! Might have to get a new one, I think mine might be a little worse for wear.