Betty, do you have any sort of big flourish set? If so, you could do the flourish with a smaller starburst-type image to evoke fireworks, and add a 'Yay!' or 'Hooray' with an alphabet set.
To illustrate, here's something along those flourish-y lines that I did as a
quick any occasion card with SU!'s Baroque Motifs; I always thought that, using a different color combo, the flower image would look like fireworks, especially if it were heat embossed in silver or gold. . .
Good luck--and be sure to tell us what you came up with!