I'd add insurance to that list, if you don't have it already.
A smaller bag to carry the lens is also nice to have - LightWare, Tamron, and others sell soft bags/cases that are more convenient than the huge Canon hard case.
Also, I have the RRS foot replacement for my 300 2.8 and it's convenient because it takes up less room, the plate can't get loose or twist, etc.
I didn't care for the Lenscoat, personally, but they graciously refunded my money. I just found it too conspicuous (read: redneck) for use anywhere other than the woods, and the covers over the controls were really annoying. Sure, you can cut them out, but for $90+ it just didn't seem right. Obviously they sell a lot of covers, so I'm probably in the minority here.
Also, both extenders, if you don't own them already, and possibly the 25mm extension tube if you shoot close subjects.