Depends on the type of RVer you are. The weekend warrior does not wander far & does not need to carry much. The fulltimer & extended traveller needs to carry all kinds of stuff.
Spares are no good to you when they are 1000 miles away. Some of the heavy things that are not used on a daily basis include, a toolbox weighing at least 50#, a spare trailer axle (that's right), 2 trailer brake drums with bearings mounted, 2 trailer brake plates with pads, a multitude of other spares such as lug nuts, spring bolts, U bolts, water pump, landing leg parts & other small stuff.
Then there is all the regular camping stuff. The chairs, bikes, genny, hoses, 100' worth of shore power cable, cleaning supplies etc.
It all adds up.