I have never hammock camped but I do backpack. I tried garbage bags and alway ended up ripping one. I hate pack covers so I purchased one of those HUGE ziplock bags and use it to line the inside of the backpack with it. I place my gear inside and zip it up. Then I just place it on the ground tarp.
The ziplock bags are pretty heavy duty, no rips in them yet from tent poles or stakes. They are even big enough to protect my hubby's larger pack - I can't remember how many liters it carries off my head.