If it's a rear radiator I'd replace the serpentine belt while the engine is cool and save the old belt as a spare. There is no reason to change the air system filters yearly but you do need to change the air dryer since you have no idea how long it's been on there. The air filter minder should give you a good indication of the condition of the air filter but here again you have no idea of how long it's been on the engine. I've bought them on eBay for less than $100 delivered.
I probably carry more spares and tools than most but I plan on keeping the motorhome for another 10+ years and do all of my own work. My most often used tool is a IR temp gun. I just went outside with it and pointed it up and got a temperature of 4° which would be about 25,000 feet.
Besides spare fluids and filters I carry a spare alternator and a spare electric fuel pump for the generator. You put the fuel filters for an ISL on dry and then turn the key on several times for 30 seconds to prime the fuel system. I change mine when the engine will not produce 100% power on Long Hill's and I've been known to do it on the side of the road. Other than the alternator I do not carry any spare parts for the ISL or the Allison tranny.
