Lived in America for a year and a half in Michigan (about 3 hour drive from Chicago). Having been to Chicago in February, can confirm it is possibly the coldest place I've been to. However, it was lovely when I went back at the end of May,.
Don't take the bin with you, I'm sure it'll be provided wherever you go. If you like your cup of tea, take your kettle, as these are almost impossible to buy in the States (take some teabags too, as Amnerican tea is dire). Other food items difficult to get hold of include salad cream and decent chocolate.
Electrical items are generally cheaper in the U.S., so you may want to weigh up the cost of shipping. If you enjoy cycling, and currently have a nice bike, you may want to ship that, as there's a load of nice places to bike in the summer. I sold my car before I went, have to say it didn't make a lot of difference as we only got 2 weeks holiday after working for one year, so only made one trip back in that time. Car insurance is generally a lot more expensive in the U.S. You may want to join the AAA out there, as this gets you free maps, and loads of tourist info if you're planning on doing a lot of touring. Get discounts and car rescue too (American garages are generally dire and take a long time to fix your car).
Above all enjoy yourselves, and don't forget to pop in a visit to the Shedd Aquarium (one of my favourite places).