1) You are physically on your own. All food, water, and supplies must be either carried by you alone, purchased from a store off-route, or filtered from in situ sources along the course. No "coincidental" prearranged support, psychological or physical. If you bonk, get lost, or have a major mechanical or injury, have the knowledge, wherewithall, and ability to get yourself found and saved without the assistance of others.
2) Follow all LNT guidelines. No gel wrappers left on the trail! Knowledgeable violation will lead to a DQ and lifetime ban.
3) Be a good citizen. Interpret #1 within reason. If you see fit to give a fellow racer directions, mechanical assistance, water, a tube, or moral support, do so. Similarly, do not expect or feel entitled to any of the above. It's nice to have good neighbors, but there isn't a law mandating it.
4) Obey all laws, natural or man made. Don't be mean to hikers, cut off cars, or ride bikes off trail.
5) On "teams". If two or more riders wish to start and finish as a self-contained unit, especially if an asymmetric share of certain burdens is pre-planned, do so intentionally. Similarly, if riding together for the last miles eases the existential pain, feel free to indulge. Finishing ranks will be listed as ties. No hangers on is all I'm sayin'.