Nobody knows what the weather is!
Luggage and bags: For a Christmas spree, never forget to bring extra bags!
Clothing/Shoes/Weather Gear: During Adventsmarkt visits, wear comfortable and warm clothes and shoes. Folding umbrella has always space in your bags. Rains might surprise you.
Photo Equipment: Cam is a must!!
Bring good walking shoes
Luggage and bags: The amount of luggage is up to you but if you plan on using the railway system to get from the airport to downtown Stuttgart or a nearby hotel, I would suggest packing in a way that you can pull or carry your bags. I had seen a few people try to pull two suitcases and have two carry-on bags over their shoulder. It appeared rather difficult to maneuver with the other passengers around.
Clothing/Shoes/Weather Gear: Walking shoes would be a good recommendation. If you wear tennis shoes, be warned that you will stand out as either a tourist or an American. Not many people wear tennis or running shoes in Stuttgart.
Toiletries and Medical Supplies: If you have allergies, bring plenty of medication. Although there are a few small drug stores, if you require special medication - bring it. Otherwise, the stores carry medication similar to that in the U.S. such as Claritin.
Photo Equipment: There are tons of sights to see and many architectural wonders in Stuttgart so I would suggest bringing a camera with a zoom lens.
Miscellaneous: New Palace & Palace Square is a must see.
(Neues Schloss & Schlossplatz)
No big deal
Luggage and bags: You don´t need anything spectacular unless you intende to go mountainclimbing in the nearby towns.
Clothing/Shoes/Weather Gear: Stuttgart experiences relatively cold winters accompanied ba snow especially in Dec & Jan. For this matter you may need warm shoes if say you want to visit the Chritmas market. Otherwise, summer is warm enough with temps ranging from 20 to 28.
Toiletries and Medical Supplies: You can obtain everything at normal prices
Goggles too, maybe?
Miscellaneous: If you plan to do what I did all night long (see: Warnings) I would definately recommend bringing your favorite mop and perhaps a small hand towel. Stuttgart seems to be made entirely out of concrete which we all know is not the most absorbant of materials, so a good quality mop with a sturdy, non-slip rubber handle would be a smart addition to any drunk's travel kit.
Luggage and bags: Backpack - most definitely a backpack!
Clothing/Shoes/Weather Gear: Even in the summer - dress like it's fall. I don't recommend any type of shorts unless you plan on hiking, and even then, make sure you take a sweater with you and/or a jacket that can be tied around your waist. The most awe inspiring views are often the coldest.