Jonathan's advice is the best for now. Anyway, in the next few versions we hope to make it easier for level designers to add custom objects that the player can collect via a better scripting API.
Also, we're aware that scripting is very underdocumented right now. Sadly, with there being a lot work to do to get a playable game shipped, that's not our highest priority. However it's very important and we'd be happy to see people working on at least some basic scripting docs/guides. It doesn't even need to be/shouldn't be too programming-focused, but just so the user can get started.