I think it's me. Almost any textured object that retains its shape when wet will do. Sponges are especially fun to play with because they come in so many different textures.
Leaves are so varied in shape that they, too, can add interest to a boring area.
Experiment with different types of paints and surfaces. Watercolors, acrylics, inks, even oil paints can be used for printing. You will generally get a clearer print on a smooth surface, but canvas or textured watercolor papers will also work. I like illustration board, which is what I used for the sample. Some objects will print with thick paints, others require the paint to be thinned.