For my son's 4th party we had a tye dye party.
We had all the plates, napkins, cups, and table cloths in tye dye. We bought tye dye shirts and tye dye tattoos and gave those out as party favors as soon as each child arrived. They were only $3 each and that is actually cheaper than a lot of party bags and less candy of course (not to mention the child can wear the shirt again). Then I bought several different colors of washable hair paint and painted each child's hair in a tye dye theme. We even had our local bakery custom make a tye dye cake. for the ice cream we had several different flavors of sherbet and sorbet for "tye dye colors". Even though my son is only four he thought it was the best party he ever had. We even had about 75% of the adults join the fun and wear tye dye also.