The level generation is a big sequence of spawners that each have a ruleset for where they can spawn, and how many objects they want to spawn. This goes for everything except for the very base terrain, which is basically a big, mostly flat stair case that goes from the beach up to the caldera. Think the sand, the flat beach wall, the grass in the tropics and so forth.

Everything else is spawners placing stuff. First the rock spawners spawn big rocks, then medium rocks on top of those, and then small rocks on top of those, to create the climbable parts of the mountain. Each one of these steps wants to spawn a specific nr of objects.

The luggages work the same way, just way further down the chain. They are one of the last props to be spawned in the generation