Some of these early pieces were on the big side, or overly specialized, and therefore not super flexible. Those steps, for example, were made for a certain place in 2-1, and didn't really fit anywhere else.
Some wall and corner pieces.
Since it would be kind of boring to see nothing but grass and rocks, I drew some flowers. (By the way, at this point the prototype character sprites were getting replaced by Edmund McMillen's designs. These, too, have been replaced for the final game.)
And a door for coming and going. And a ladder, although we didn't stick with this design.
And a tree. I had this idea to make the tree really useful with these Swiss Army Knife-like appendages. The extensions were separate pieces, so they were all optional. As it turned out, there wasn't much use for them at all! The tree is still in the game, but without the branches.
Click image for full size.
Here you can see how those pieces fit together into a level layout. This is still just a Photoshop mockup, though. The grass, rocks and flowers are in a foreground layer, and I was painting the vista in a background layer. It was important to work with the foreground right there, to ensure all parts would relate properly, just like different elements of a painting.