Michigan is known for being very cold, and it is during the winter. However, during the summer, it can get very hot and muggy. Wool is usually the best material for cold weather, and cotton is usually the best for hot weather.
Photo Equipment: There are a of of great photo oppurtunities downtown and in other areas. Detroit has a large collection of beautiful early 20th century skyscrapers.
Miscellaneous: Make sure to bring a sense of adventure and don't be afraid to thoroughly explore the city.
Bring comfy shoes, there's a lot to see in the city but you're going to have to walk a bit to get there.
Toiletries and Medical Supplies: There are hardly any "corner stores" in the city. Especially in the heart of downtown. There are a few CVS/Wallgreen's near WSU's campus. So if you need any asprin or anything else along those lines get it before you get in the city.
Photo Equipment: I always bring a camera everywhere I go, Detroit is no different. There's plenty of fun, odd, pretty...things to take pictures of!
Camping/Beach/Outdoor Gear: No camping or beaches that you're going to want to hit up if you're here to visit Detroit but as far as outdoor gear bring a coat, no matter the month. Yeah sometimes the summer is hot but downtown it usually windy.
Miscellaneous: Bullet Proof Vests are a MUST!!!! I would recommend a powerful handgun, dressing ghetto and driving a crappy car with Michigan plates so you don't stand out for Detroit's army of muggers and professional car stealers! It may sound funny, but last time I was in Detroit, my car was stolen right in front of me!!!!!!!!!!
Sudden rain storms happen frequently in the fall, so be prepared for cold & wet.
Photo Equipment: Black & white film is great for the old downtown buildings.