How should I do my hair for a formal event?

Tomorrow is my confirmation; I don't know how big of a deal that is in other countries, but in Croatia it's a very important and formal event. All your family members, even the distant ones are going to be there, the boys are all in suits or tuxes, the girls in dresses and heels... My problem is that I have no idea what to do with my hair. It's very hot here, and the confirmation is going to go on for at least 2 hours, so I'd suffocate if my hair is loose. I was thinking maybe a bun or a braid...Any suggestions?