Are you going to make them yourself? If you are going to use (or know) a florist, ask him/her, even if you aren't thinking floral centerpieces -- they have great ideas, and they are happy to help even without flowers or plants.

My son's bar mitzvah was at Purim, so we had a masquerade party, and we had collections of masks, beads, face paint, hats, etc. in the middle of each table (not just for decoration -- for guests to use, especially the ones who had refused to wear costumes but then regretted it once they arrived!), and just a little vase with a gerbera daisy and some ting-ting in the middle. The florist arranged it all. For my daughter, who had used part of her money to buy school supplies for a school where she volunteered as a tutor, the florist arranged some of the notebooks, crayons, etc., along with a little note explaining, in the middle of the tables for the kiddush lunch. I have seen similar displays with donated books, toiletries, and toys.

Mazal tov!