What Spares to Carry for C-18’s?

I think that is still a belt driven alternator? Then a spare belt set (two).
Secondary and primary fuel filters.

Unlike the ole Detroits, I don't think you can not change out an injector without the Cat software in a laptop.
I don't think one of those injectors will store well anyway.

Belts, impellers, fluids, primary and secondary filters. I don’t carry a spare raw water pump for the C32s but I do carry both spare impellers and one pump for generators because of how much they run

I ve been considering carrying a spare starter now that they are 10 years old.

On the later Cs and ACERT, is there still a hand fuel pump.
After 3412Es, I have not noticed a hand pump and on my last few C32s, nope, no hand pump.
Last Hand pumps were on 3126s that I noticed.
Time to crawl down in your E R, Sit down on a 5gal pail (with a pad hopefully) and start talking to your new girls. Look for that fuel hand pump. It is a real genie when needed.
A tight beam flash light helps. Everything you turn it on to, needs to be understood in your and mate (next engineers) mind. It takes two to run a boat when there is an issue.
Another sip, turn on flash light in another direction. what ever the light lands on, understand what that is and how to service it.
This is why it cost my new customers a bottle of rum, 20 hours, band-aids and new leagle note pad thru their off weekend and how I learned their boat. By Monday morning, I knew their boat better than the MFG. Doctors have nothing on me, I can read my notes and scripts (and only I).

40+ years later, I still answer questions on boats I used to manage or worked on.

On that point, every time I used my hand pump on the c15's it needed to be replaced, losing its seal, allowing air to be introduced. They were a real SOB. Yes, carry a spare pump aboard, too, unless Cat advises this historical issue has been corrected. Eventually I plumbed my transfer pump to be used to prime the engines so that I never had to touch that forsaken hand pump. Serves a great purpose, but is kicks your shin, too. I hope they remedied this...

Oh, and pencil zincs.

We do zincs at every oil change so I don’t carry them. Away from home I try not to do any maintenance unless it’s needed, always a risk of something going wrong

our 2009 C32s have the manual priming pumps, I ve used them a few times to make sure they work but when replacing filters I use the electric priming pumps. A must in my opinion

At the point of fuel return there is a check valve that restricts fuel to support the pressurized rail. I actually installed a t-ball-valve at the hose ahead of this check valve which allowed me to push fuel completely through the filters and rail system, clearing all air, and minimizing cranking. Of course you have to return the valve to the check valve flow position prior to that cranking...but it was foolproof if you didn't foolishly leave the valve in the bypass mode...

I would check the zincs monthly, to start. On a set of 3406's I took care of, the lower heat exchanger zinc was completely gone to a nub in 30 days, but all others remained serviceable. That yacht sat at the dock most of the time during winter, and the engines were run to near temp, in gears, at the dock bi-weekly.

Remember, the engines are covered by an extended service contract. For the owner to get into the fuel system or any engine/clutch modifications may be a no no.
The best the O P can do is take care of consumables and have enough duct-tape on board to cover any emergencys to get back to a dock.

You're absolutely right. Owner shouldn't touch. It was more a continued discussion about the priming of these...