For ease of use and comfort, nothing has beaten our REI Infant Down Suit in the wintertime. It works pretty well in most colder temps due to the fact that you can unzip and fold down the front to cool or zip it up to the chin, and you can throw the kid in there without a lot of layers because the down is pretty warm. Hands/feet fold in or out so you don't have to put shoes/gloves on. Unavailable right now but I'm sure that REI will have a new model out in a few months for the winter season. #1 pick for me.

Ditto on the Timbuk2 bag. A nice messenger bag is suitable enough to carry all your junk, waterproof in case of interior or exterior spills and much less dorky and re-usable than a diaper bag.

One of the foldable diaper changing mats with a small amount of room for storage is great. You can lay it out on any flat surface or dirty changing table to give a nice area to change. Something like the ones below:

http://www.amazon.com/Built-NY-Cushy-Cha...280&sr=1-25
http://www.amazon.com/Kalencom-Quick-Change-Kit-Doodlebugs/dp/B001P5HLWO/ref=pd_cp_ba_0
http://www.amazon.com/Kiddopotamus-Chang...280&sr=1-47