You're so excited, you'll dress up specially for it. And you will wear bells. Figuratively, of course. :)

With enthusiasm, energy and emotion... ready to go and participate. (-:

"with bells on" means you do it with a lot of interest and energy (with a lot of enthusiasm)

I'm looking forward to it. I'm not coming because it's an obligation. I'm coming because I want to be there. I will be very enthusiastic / ready for fun.