I used to "sack" and itemize all my gear. It's nice for organization, but adds 8-12 oz or more, and it's unnecessary.
Try some of these ideas:
Sleeping bag in it's own separate dry sack; all other gear in a trash compactor bag.
All gear in a roll-top dry sack, not itemized in individual bags.
All gear in a trash compactor bag.
Small ditties in ziplock freezer bags or cuben sacks.
Pack cover (not the best plan for heavy rains, IMO)
...or any combination of the above.
I do think it's advantageous to have your sleeping bag in it's own separate dry sack, because this is a critical piece of gear you never want to get wet. Sure, a trash compactor bag does the same job, but I like that extra layer of security around my bed. Nothing worse than "surprise!!! there's a hole in your trash bag and now a wet spot on your sleeping bag".