Figure: PAC Region, from Eddie's notes.
Regional differences from the ICAO standard can be found in ICAO Document 7030 and your Jeppesen Airway Manual. Both of the sources, however, can be out of date. See International Operations Manual / Regional Introduction for ideas about getting up-to-date information.
As countries around the world update navigation systems and procedures, it becomes increasingly important to speak with somebody who has been to the airport recently or have a contact in country with local knowledge. As we say in the military, there is no substitute for boots on the ground.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
This region is moving from a mix of navigation requirements to the system of Performance Based Navigation outlined in ICAO Document 9613. Current navigation requirements are available on Jeppesen Airway Manual Air Traffic Control pages and Chapter 4 of each region covered by ICAO Document 7030.
[ICAO Doc 7030 Amendment 1, §MID/ASIA, ¶18.104.22.168.]
Most of the Pacific is under RNAV 10 (RNP 10) but there are parts that have gone and are going to RNP 4. Aircraft without RNP 4 are still allowed, but those with it have traffic priority. More about this: International Operations / Required Navigation Performance 4.
[ICAO Doc 7030 Amendment 1, §PAC, ¶22.214.171.124.]
Keep in mind RNP 10 is an exception to the rule of Required Navigation Performance standards, "RNAV 10" retains the "RNP 10" designation for matters of convenience.
Most countries in the Pacific Region are WGS-84 compliant but some are listed by Jeppesen as "unknown." You should check the country's Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures pages and the http://www.jeppesen.com/company/publications/wgs-84.jsp web site before visiting Nauru, Papua New Guinea, or Timor Leste. More about this: International Operations / World Geodetic System 84 (WGS-84).
[ICAO Doc 7030 Amendment 1, §PAC, ¶4.2.1.] RVSM shall be applicable in that volume of airspace between FL 290 and FL 410 inclusive in the following FIRs: Anchorage Arctic, Anchorage Continental, Anchorage Oceanic, Auckland Oceanic, Easter Island, Los Angeles, Nadi, Oakland, Oakland Oceanic, Seattle, Tahiti and Vancouver.
More about this: Procedures & Techniques / Reduced Vertical Separation Minimum (RVSM).
Some countries use non-standard transition altitude and transition level changeover procedures. In Brunei, Nauru, and the Solomons, for example, the changeover occurs geographically. More about this: International Operations / Transition Altitude / Layer / Level.
[Jeppesen Airway Manual, En Route Data, Pacific, Australian Organized Track Structure (AUSOTS), 26 Nov 2010]
[Jeppesen Airway Manual, Pacific Ocean High/Low Altitude En Route Charts 3/4 P(H/L), 12 Oct 12]
[ICAO Doc 7030 Amendment 1, §PAC, ¶126.96.36.199.]
Note.— PACOTS guidelines containing detailed information on track generation, lateral track spacing, level assignment, position-reporting requirements and other relevant details shall be published in the AIPs or associated supplements of those States which utilize a flexible track system within their airspace or areas of responsibility.
Note: the PACOTS require RNAV 10 (RNP 10) Navigation Performance.
[Jeppesen Airway Manual Air Traffic Control, State Rules and Procedures, North Pacific (NOPAC) Routes, 7 Jan 2011]
Each country departs in some ways with the ICAO standard and common US practices. Pilots should always refer to the Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures pages for each country on their itineraries for differences with ICAO Standards, Recommended Practices and Procedures. More about this: International Operations / US versus ICAO.
The following are a sampling of some of the differences, there are many more. You should check the Jeppesen Airway Manual State pages for every country you takeoff, overfly, or land.
[ICAO Doc 7030 Amendment 1, §PAC, ¶9.3.]
9.3.1 The following procedures apply to aircraft operating in the oceanic airspace of the Anchorage Oceanic, Auckland Oceanic, Nadi, Oakland Oceanic and Tahiti FIRs. These procedures are intended to complement and not supersede State procedures/regulations.
9.3.2 In the event of total loss of communication, an aircraft shall:
a) try to re-establish communication by all other means;
b) if all attempts to re-establish communication with ATC are unsuccessful:
1) squawk 7600;
2) if able, broadcast in the blind at suitable intervals: flight identification, flight level, aircraft position (including the ATS route designator or the track code) and intentions on the frequency in use, as well as on frequency 121.5 MHz (or, as a back-up, the VHF inter-pilot air-to-air frequency 123.45 MHz);
3) watch for conflicting traffic both visually and by reference to airborne collision avoidance systems or traffic displays (if equipped);
4) turn on all aircraft exterior lights (commensurate with appropriate operating limitations);
5) maintain the last assigned speed and level for a period of 60 minutes following the aircraft's failure to report its position over a compulsory reporting point (including ADS-C flights), and thereafter adjust speed and altitude in accordance with the filed flight plan;
Note.— In airspace where the strategic lateral offset procedures (SLOP) has been authorized, aircraft experiencing communication failure may also elect to initiate SLOP in accordance with State AIP, including an offset of 1.8 or 3.7 km (1 NM or 2 NM) right of track.
6) Upon exiting oceanic airspace, conform to the relevant State procedures and regulations.
In the event of lost communication, ATC shall maintain separation between the aircraft having the communication failure and other aircraft, based on the assumption that the aircraft having the communication failure will operate in accordance with the procedures in 9.3.2.
These are exceptions to ICAO Lost Comm procedures. More about this: Abnormal Procedures / Lost Communications.
Some countries have uncontrolled IFR airspace requiring a "listening watch" procedure on air traffic advisory service frequencies. For one example of many:
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, Fiji, 3 Oct 2008] The VHF RTF frequency to be used will be promulgated by NOTAM, however, in the case of temporary disruption occurring in controlled airspace, the VHF RTF frequency to be used within the limits of that airspace will be the primary frequency used for the provision of an air traffic control service within that airspace.
The TIBA procedure in New Zealand is fairly standard but the frequency selection can be a chore. Refer to the Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, New Zealand.
For more about this: International Operations / Traffic Information Broadcast by Aircraft (TIBA).
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2 2008
ICAO Doc 9613 - Performance Based Navigation (PBN) Manual, International Civil Aviation Organization, 2008
Jeppesen Airway Manual