A ground cloth is a neessity.

1. it keeps you and your gear dry
2. it keeps you cleaner,
3. it keeps little things like batteries, etc. from disappearing in the forest duff when you drop them
4. it keeps wear and tear on equipment down.

There you have it.

I'd get the lightest fully COATED ripstop you can find. You can get polyurethane coating or the lighter double coated silnylon. Avoid single coated silnylon.
Avoid Tyvek - it picks up ALL kinds of tiny forest floor debris in its fibers.

"There are no comfortable backpacks. Some are just less uncomfortable than others."