I've begun to add sound effects. Mainly, effects are in place for walking on terrain, as well as for certain menus. I have adapted the sound engine from Venture the Void, which is called "Aurex". I should GPL it sometime, because it's a very clean, well-thought-out engine for game sound effects that integrates well with SDL.
The system is in place for picking up and carrying things, as well as dropping things. It required a bit of mathematical thinking in terms of what it means for an item to be on an area, vs. dropped by the player, but I think it's worked out.
Next I am going to create a document, "elements", in which I will try to create a plan for weaving the gameplay elements together into a fun fabric. I don't want to base gameplay too much on the crutch of existing systems, but at the same time I'd like to develop something resembling a scientific approach to evaluating whether they are fun. The model for fun I will use will be based on the idea of play as an exercise for real human survival. So when trying to decide if something is fun, I will think about whether it's exercising (or emulating, as this is a role-playing universe) a survival skill. That might be a weird way of looking at it, but that's the most convincing explaination of fun that I've read yet!