M.L.
Most souvenirs seem to be made rather realistically, rather than modern and graphic-arts-ish.
Have you come across pictures (online) that you like? I wonder how it would look if you printed out the pictures and wrapped them around small boxes (of the proper size) which you could stand upright - or however - on the table. Admittedly it seems weird in written form, but it looks good in my mind! You don't have much time to prepare, so it might be an easy way to decorate as well.
It sounds like a lovely party, and if I lived on your side of the country I'd hope you'd invite me.