how to sequence tenses in type 2 conditional

[ostap77]

Do I need to put everything in a past tense in the main clause in type 2 conditional?

"If I went out to diner with my friends, each of us would pay for what we've/had? eaten."

 

[Tdol]

I'd use the past perfect.

 

[ostap77]

I would assume either is possible. Is it mandatory to backshift to a past tense in the result clause?

 

[Raymott]

I would assume either is possible. Is it mandatory to backshift to a past tense in the result clause?

I don't think you're backshifting. It happened in the past, so a past tense is apprioriate (not present perfect).
"If I went out to dinner with my friends, each of us would pay for what we ate." That's simple past, which is OK (for me), but the past perfect is also correct.
The rules for the second conditional only stipulate the tenses in blue. For example, the following is also Conditional 2.
"If we bought the tickets today, we would pay for what we are going to see tomorrow."