Best peeps to ask are the organisers, the last ODE I did many years ago and unaff, we could ride in spurs, but no whip! Otherwise usual dress for dressage and snaffle bit etc
Pony Club rules are quite strict, you really need to find a rule book.
If you haven't got time, sort out all the tack you have - e.g nosebands, etc. and then when you get there ask the Secretary or another competitor for a look at the rule book. You don't want to get eliminated just for having the wrong tack.
One thing the Pony Club don't allow is coloured tack. I had to go out and buy a new noseband when I took my horse to a PC competition (with adult riders class) as she had a white star and her normal noseband had white piping, which I thought brought out her star very nicely!