Not sure if you have an idea for centerpieces yet - but i saw you posted seed packets for favors and thought, hey! What about watering can centerpieces with flowers in them? You could do different watering cans for each table - attach a table number to it, and done. Fun and cute, yeah?
Pretty Pouches for Wedding Favors - "It's sew simple: Cut a rectangular strip of fabric to the desired width (allow for a 1/2-inch seam on both sides) and twice the preferred height. Fold the fabric in half with the right sides facing, stitch up the sides, and turn the whole thing inside out. Use pinking shears to finish the top edge, and fill with treats. Fashion ties out of fabric that's been torn on the grain."