I'm relatively new to diesels, and am trying to put together a tool kit and required spare parts for my 06. I carry all kinds of parts for my Bronco when I go wheelin, but I've found out where the weak links are over a decade of ownership. I don't know where the common failure points are on the Dodge yet. My CTD is primarily used for daily driving and towing (not for offroad since I have a dedicated truck for that). I also need to consider spare parts for my trailer.

I was figuring on the following parts and tools as a starting point:

Truck:
Fuel filter
serpentine belt
rear axle u-joint
basic tool set (I need to get a larger socket set with 1/2" drive sockets for fuel filter)
4 way lug wrench (large)
tow strap
jumper cables

Trailer:
Spare hub and wheel bearing assembly
Spare electric brake parts
Grease
Extra receiver hitch assembly (non weight distribution) and pin
Light bulbs (or swap primary lights to LED)
Basic wire and connectors to repair electrical issues

I don't want to carry a ton of stuff, but if it should be in the box please post your suggestions. If I could fit it all in a decent sized too bag behind the seat in my regular cab that'd be great, but I'm planning on having a box in the bed. Is the factory jack adequate for changing tires? I don't have a separate jack for the trailer. If I have my Bronco on the trailer there is a very comprehensive tool kit and hi lift jacks.

 

You have a pretty good list there already.

Carry 2-3 fuel filters. If one plugs on you, then you'll probably be changing it a second time shortly thereafter (because you'll still be running the bad tank of diesel through the first filter).

In addition to everything on your list, I also carry:

Air filter (diesels in general go through air filters and they need to breathe heavily)
Oil filter (probably not really necessary, but just in the remote event I need it)
Oil filter wrench
2 quarts of extra oil (never needed it though)
Tire plugger kit
Multimeter
Air compressor
Trucker's chain

I carry a lot of other junk in my truck, but that about covers the "tools and spare parts" portion of my junk. I've used the factory jack twice to change tires on my trailers and it gets the job done.

 

As a suggestion, I would recommend using Evans coolant, it allows you to use a no pressure coolant system. If you ever have a hose, clamp issue it will be a small drip and not the gusher I have had with a pressurized system.
If you are off road, or travel a great deal, to me it is worth the peace of mind