I use a mixture of dead leaves, coco fiber, and organic potting soil in all my setups.

The only one that has a proper drainage layer is my skink tank though. Drainage layer is separated with egg crate cut to fit (as a sturdy barrier for burrowers) and nylon window screen to keep the dirt out. Isopods, red wigglers, and springtails added, along with sturdy plants that will tolerate low light. I haven't attempted anything fancy with waterfalls and such yet, but I'm planning a larger setup for some milk frogs that should end up having one.