in short - anything that will allow water and air to pass through, but not soil can be used as long as it is non toxic, non corrosive, and meets the previously mentioned requirements.

Commonly used items include

Brand name Drainage barriers from companies like Zoo Med or Exo Terra
Nylon or Fiberglass windows screen (I prefer fiberglass because I worry about the Nylon screening getting brittle of time but that may be a false worry)
Weed Block (though I feel like this does not let the water pass through fast enough sometimes and can lead to soggy soil)
Quilt Batting (thanks Lynn!)
and anything else that meets the previously mentioned criteria.

If you come across something you want to try post it on the forums. Someone else may have tried it or someone may know a reason to steer clear for it.