Whisky.
Spades/shovels to clear a spot for your tent if it’s not all thawed.
Some way to clean the bike(s) a bit is good, since the queue for the bike wash can be massive.
We had a gas space heater in a marquee last year, and that was excellent (til the fan broke and the gas ran out!).
Woolly travel rugs are good for your lap when you’re sitting about.
2nd TJ’s comment about a watch/alarm clock. Nothing worse than getting back from beasting a lap to find your pit area empty or in disarray!