I use leaf liter from Black Jungle Terrarium Supply or Joshsfrogs.com. I like the Live Oak leaves for dart tanks since it retains moisture like little cups.
There are a few versions of bromeliads that stay small and you could actually get two or three of the small ones in there for the frogs to climb on and hid in.

Here re some small Broms I grabbed up at Black Jungle one day...
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