Question for ETOPs experienced guys

[300-600]

Once you have dispatched and the MEL ceases to be applicable what are the technical issues that would prevent you entering ETOPs airspace.
I believe loss of two LRNav systems is a no go for MNPS airspace,
The fuel crossfeed must be operational for a 767 (AA diversion into JFK due to this).
APU and fuel crossfeed required for 737 (138 mins ETOPs)

What else are you not permitted to enter an ETOPs area without.
How about a single pack operation? Is this Captains discretion.

We have a section four bolted onto our MEL which gives things you cant dispatch with ...but no guidance after dispatch regarding technical defects.

Any thoughts much appreciated.

[RMC]

Each aircraft has its own ETOPs redundancy requirements....some, as you say are generic. I know what they are on my aircraft type from training...but cant find where these minimum items are AFTER the aircraft has dispatched.Prior to dispatch they are found in section four of our MEL (mostly air conditioning items there).