I think, for example in 69F class H.S.R.

ISSA Procedural Rules - https://hssailing.org/documents/ISSA-PR-2021-2024.pdf
ICSA Procedural Rules - https://collegesailing.org/documents/ICSA_Documentation/2021-2024_Procedural_Rules.pdf

Many one-design classes also have championship conditions for their national / continental / world championships which may be invoked.

Thanks Matt, I forgot about the Procedural Rules.  

Lately individual venue COVID rules have become popular to invoke as Rules of a regatta. Hopefully that's waning but it has seemed to be a good way to draw attention (and consequences for violating) to what helps hosts be comfortable hosting events at all.

Basically, any document the NoR lists as rules is a "document governing the event."  Many championships (e.g., US Sailing championships) have Championship Conditions, which are invoked by the NoR and thus become rules.  As Matt says, most classes have championship conditions, which may or may not be part of the class rules.  Some events have special Codes of Conduct.  The list goes on.  How many of those say anything about the ERS is another question.

The deed of gift for a trophy.
The US Sailing Regulations
The US Sailing Championships Conditions
The U.S. Youth Match Racing Championship Conditions
The Championships Code of Conduct
The US Sailing SafeSport Handbook.
Class Bylaws
Support Vessel Regulations

Some more potential 'other documents' (b references the Notice of Race, SIs, so already covered).  The references to RYA are obviously specifically UK but I'm sure other regions would have something equivalent. 

As I understand it, a boat can only be protested if the reason for protest is specifically mentioned in the Notice of Race.  So a boat could, for example, break the law and be prosecuted for impeding the progress of our biggest aircraft carrier in the approaches to Portmouth or a giant container vessel in approaches to Southampton but the race organisers can do nothing about it and the boat's race result would stand unless the relevant by-law is listed in the NoR, which has potential to cause conflict with those who share our waters.  Other documents address items that aren't covered in the RRS &/or where World Sailing has published relevant appendices, particularly relating to offshore racing (safety, night, virtual waypoints).

Hi Kirsteen.
As per crossing the path of a aircaft carrier, you can refer to the preamble of part 2 of RRS:
 ""When a boat sailing under these rules meets a vessel that is not, she shall comply with the International Regulations for Preventing Collisions at Sea (IRPCAS) or government right-of-way rules"". 
and you can DSQ a racing boat,  for sinking the aircraft carrier.

For any keelboat race that goes out of sight of the race committee, the Offshore Special Regulations
https://www.sailing.org/inside-world-sailing/rules-regulations/offshore-special-regulations/

A nautical chart may be a document governing certain types of events, such as a keelboat race.
(See RYA Case 1989/6)
To note, that chart must be listed or referred to in the NoR or in the SIs before it becomes effective for racing boats.
(See RRS J1.1(3), WS Case 98, and RYA 1989/6 itself)

Regattas that are held on impoundments controlled by the US Army Corps of Engineers may have further restrictions on events held thereon.  Restrictions on the type and wearing of PFDs comes to mind as an example.  These would need to be enumerated in the NOR/SIs as well.

All kinds of things, it seems, may be included in the Rules under Def (g). Listing them all sounds like an exercise in futility. A good rule of thumb is to learn what the sailors need to have a safe, fair, and fun event, and provide it to them. Government (at any level) laws and regulations, of course, always apply and to mention them (e.g. Don't sail thru a mooring field) is a courtesy. If I'm running pretty much any event, I look to the OA (and Class if they're not part of the OA) for some good insight as to what special docs need to be included to tailor the event. It sometimes takes a little digging, but it makes for a better experience for the sailors, and they are, after all, our ultimate customers.

interesting conversation