To answer your question directly: there is a member 20% coupon with our Anniversary sale! If you're looking at the Osprey Ariel or Aether backpack they are included in the Anniversary sale (page 8 of the catalog), so you could save that coupon for another item.
In terms of your question about dividends, you are not able to apply two dividends into one transaction on REI.com. If you have any other questions about your membership or dividend, feel free to reach out to our Sales and Customer Service team at 1-800-426-4840 or via Live Chat.
Hope this helps, thanks!