The ideal rings for use in completing the Endboss (Shallow Seas) is as follows:
Mantis, Hack, Slash, Wish, Bandage, Meat, and two buffs.

Each member of the crew should have two different buffs. No person should have a same buff ring. To make this easier, clans or other usual crews should develop a system where the same two buffs are paired the same way every time.

My clan groups them as shown:
Teflon Spray / Coyote Spirit
Ghost / Iron Will
Improbability Sphere / My Density
Rock Armor / Healing Halo
Pot Lid / Keen Aye

Crew members are responsible for developing rage up to RR4 before you enter the whirlpool to go to Shallow Seas. This can easily be done by fighting the Sand Castles, Anchor Bugs, and fluffs on Gold Beach.

When all crew members have reached Shallow Seas, all crew members should use the first buff of their assigned buff pair at RR4. (Look back at list to see the first of each pair)
Then RR1 should be used for your second buff. Using Meat at this point before you start is also highly recommended.

After you develop rage up to RR4 again, use your second buff at RR4.
After developing rage to RR4 again, use Meat for yourself. You'll need it.

Keep your assigned buffs at RR4 at all times. Your crew is heavily dependent on the buffs you are assigned to in order to make it through the entire run. You will also need to keep track of your RR4 Meat as you will need the additional health boost in order to survive the run yourself.

What about your other rings?
Mantis, Hack and Slash should obviously be used for fighting, everything. They have been proven to be the best rings in damage caused over time to a single target.

Wish is used to heal your crew members at all times. Your crew is heavily dependent on being healed using Wish, you are also dependent on your other crew members in returning this favor. When your two buffs and Meat are at RR4, you should spend the rest of your rage in using RR2 Wish on your crew.

Bandage should be used in healing yourself in emergency situations when your crew doesn't use Wish on you in time.