My collection of "parts" seems to constantly be growing. There's the obvious tote with fluids (motor oil, trans fluid, distilled water, etc.) as well as the "consumable items" such as filter cartridges for the house water filter, the fridge water filter, the faucet filter/aerators, fuses, etc. Then there's my growing collection of "little stuff" that I've accumulated in course of repair and upgrade projects (spare LED light bulbs, a spare serpentine belts, spare cabinet latches ... my collection of nuts, bolts, screws, washers, hooks, electrical connectors, hose clamps, etc.)
In many cases - I've got the spare item because I had one item break - and then bought an extra one for "inventory" when I went to replace it. In terms of "bigger" stuff - I carry an unmounted spare tire (having discovered that while Coachnet can usually get a mobile tire service dispatch underway very quickly - it's very possible to be stuck (for a couple of days!) because a replacement 295/80R22.5 tire isn't readily available). Last year - my hydraulic pump motor failed - necessitating a replacement by a mobile RV repair service. I had the original pump motor rebuilt and now carry that with us. The little stuff "lives" in a small plastic tote that's tucked into a basement compartment. Aside from the spare tire - my collection of spares doesn't add up to an extra 75 lbs of stuff. These days, I'm finding that I'm able to make a repair using stuff from my "inventory" - eliminating the time and trouble of having to make a trip to a local RV dealership or hardware store.