We have a U1250, and a GVM of 8 tons, your U1300 will probably be 7.5 tons. You can only carry as much spares and tools as you have spare weight for, so that would limit most thing.
We carry the things that will help us get out of some remote place, the other parts we have packaged at home, ready to ship out to where we are.
We carry a lot of patches for fixing tyres, very big ones and small one, so as long as we don't destroy it completely, we should be able to patch it. We have a TPMS, so wil get warning about low pressure and high temperature before we destroy anything. We also have spare valves and valve inserts.
We have a new UG100 gearbox, and carry a spare shift cylinder for it, as we have had one fail on our old gearbox, but were were able to keep on driving. Other than that the transmission is new so not really a concern for us, but on yours, I would add the range change valve as well.
We carry a master cylinder and slave cylinder for the clutch. We also swapped the very long steel line and long hose for a much short, steel braided teflon hose which makes it easier to bleed, but would need to be disconnected if I tilt the cab fully. We have a spare output shaft bearing as well.
We have spare portal boxes, already assembled with new bearing etc. We have them packaged to send out, but might consider taking one with us if we were going away for a while, but it is quite heavy. We have four litres of oil for the portals and the diff, and another four for the transmission. We also have spare portal seals, portal box plugs and copper washers.
The air system is quite complex, and quite reliable as long as you keep it clean. We fitted a filter/dryer to ours, which helps keep it very clean. The main things are the 4-way valve and the pressure regular. I have an 8 bar system on mine, but yours will be an 18 bar system, so not that easy to get parts. I would get all the major air system parts as spares. We also carry all the various size air lines, and joiners. We replaced all the our ferrule style with the new VOSS push-fit system when we replaced the entire air system.
We carry a full set of brake pads, the rears can stick. We got the rear pads, they are slightly different to the front ones, but could be used for the front as well. We fitted new brake calipers, and have some spare ones at home for just in case. We have spare brake hoses - I swapped mine all out for steel braided Teflon lines which are a lot tougher than the rubber one, and carry a couple of spares for the front and back. I also carry some spare steel brake tube, and ferrules for the brakes, as they are a different size to normal car or truck ones.
We have two fuel tanks, so gives us redundancy there, but was also carry some fuel tank repair putty as well. We have spare fuel filters, and we have pre-filters on our fuel tanks, we use the standard CAV filter, and have spare glass parts for the water separator. CAV filters as cheap and we carry 10 of them, as they will clog up if the fuel is bad. We can transfer fuel between the tanks through the filters, so can clean up dodgy diesel, just takes a couple of filters. We have done this twice due to bad fuel. They protect the main fuel filters and the lift pump. We also carry a selection of hose and clamps for the fuel system. We have a spare lift pump as well.
Engine wise, we carry 10 litres of oil and a couple of spare oil filters, and a spare set of injectors, just in case something gets past the two sets of fuel filters, but to be honest, that is overkill, as these engines can run on pretty bad fuel. We have a spare set of fan belts, radiator cap, thermostat, and full set of radiator hoses, heater hose and some heater hose joiners, along with some JB Weld to fix an leaks in the radiator, and some silver solder to do a better repair if necessary. We also carry spare inlet/rocker cover gaskets, as it that goes, you would loose boost and be blowing oil all over the place. We have some spare gaskets for the turbo as well.
Electrical wise, ours is a 12V truck, so easier to find the part than a 24V system. We have a spare regulator for both alternators (we have two). We also have spares for the starter motor, ours is a reduction gear one, so have spare solenoid which is the weak point on it. We have a spare starter back at home just in case. We have wire, fuses ( all sizes) connectors and terminals.
We carry a fair bit of recovery gear, with winches front and rear, kinetic rope, tree protector, winch extension, shackles etc.
Tools wise, we have everything we need to fit the things we carry.
We are weight limited rather than space limited, we could carry a lot more, but have to watch the GVM and make sure we are not over the limit.
Hope this helps,
