The minimum you should be wearing at the rally, while riding, should be sturdy, over-the-ankle boots with preferably grippy soles, an approved helmet with eye protection,gloves, long sleeve shirt/jacket, and long pants.
This will offer minimal protection in a fall.
"Real" motorcycle gear will protect better.
Coming to a rally is cool, since you'll get to see a variety of motorcycle gear being worn by a variety of people. You may see some product you were thinking of buying walking around the campground.
If you can't afford or find better gear, make the best out of what you have....but...a helmet with eye protection, long pants and top, gloves, and adequate boots are a must.