The aisle way could be decorated with bamboo torches or rod iron candleholders. You could use fresh or silk flower garlands to line the pews. Hire a bagpiper to head the procession. Rent a horse and carriage and decorate the horses with flowers. If the groomsmen are using swords, you could have them create and arch with their swords for the bride and bride’s maids to walk through.
Create a back drop behind the head table with a castle painted on it. This could be an event that could involve the entire wedding party, have a "paint the castle" night!
Create some over sized banners with the family crests or the crests of the round table for the walls of the reception hall.
You could use the green garland you can find out in stores at Christmas time. (It’s great if you can get it on sale after the season). Use the green corded mini Christmas lights entwined in the garland and cover lightly with soft white tulle. Gather the garland up in swoops and complete the look with a soft fabric bow or clusters of silk flowers.
Rent a couple of suits of armor and place them at each end of the head table.
If you are handy with carpentry, you could have a couple of thrones constructed for the bride and groom to use at the head table. Paint them gold and upholstery the seat and back with a rich velvet or brocade. You could also cheat with this concept and create a slip cover from velvet or brocade to cover a conventional chair.
Decorate the walls with shields, swords or "horns of plenty" stuffed with fruit (you could use plastic fruit).
Pewter or metallic goblets for the head table are a nice accent.
Rent a couple of stuffed deer heads for the walls.
Spray paint the long plastic stadium horns gold and mount them on the walls or use them as part of the table decorations. You could cut a small slit in the mouth portion of the horn and use to number the tables.
Silver napkin rings.
Silver or pewter goblets (you could have "bride’s maid" or "groomsmen" with the date engraved on these for your attendants).
Rosemary sprigs dipped in gold paint and tied with a ribbon.
Velvet mini sacks filled with chocolate foil wrapped coins.
You could serve the food on silver or pewter plates. If you don’t have enough, cover plates with foil. You could also use flat breads for the plate and serve big platters of finger foods (no cutlery). Some popular finger foods would include chicken wings, large strips of beef, pork, baby carrots with the stems still on, large stuffed mushroom caps, potato wedges, filled potato skins, cheeses and fresh fruit, pickles, raw veggie platter, shrimps on a skewer and fresh baguettes. Just make sure there’s lots of food for your feast.
If you opt not to have a sit down dinner, a buffet is perfect for a medieval themed wedding.
A cake shaped like a castle would be a lovely edition to the evening.