Any quick and easy to set up party room decoration ideas?

We only have 15 minutes so I don't want to go crazy but I still want to make it a little more festive! We will have extra hands on deck to help.

The party hostess will set up tablecloths and a birthday banner beforehand.

We will have to set up the cupcakes, birthday cake, some munchies, plates/cups and such. They provide the goody bags but I want to add something to them. I have a paper tassel garland leftover from a previous party I will use.

No balloons or piñatas allowed.

Thanks!