Use a stiff base like cardboard, foam board etc. Glue low relief items to it.
You can even use a hot glue gun to make marks on the base.
|the inked plate|
|rolling out ink with a brayer|
Sometimes I just brayer the top of the collagraph to catch the design. Experiment with all techniques to find the one you like the best.
|on Painted Fabric from my Fabric Transformations Workshop|
|collagraph on a T-Shirt|