What decorations should I have for a party?!

I'm hosting a surprise party at a chain restaurant and planned to bring balloons a cake and a few silly little center pieces. Aside from that I didn't think I'd need anything else, but I have multiple people volunteering to help me set up. I'd love to make this a hugely successful party but can't think of what to do.
I'm pretty craft so do you have any ideas on how I could decorate?