I made 3 large arrangements to be placed around the room. I just filled a vase with green apples, filled the vase with water, and arranged Calla Lilies, Stock, and Snapdragons.
Because I had to make around almost 140 centerpieces, I had to make 4 different versions ( I don't have 140 of one thing...) : a cylinder vase with stacked apples, two types of bubble vases with some river rocks and an apple, and a hurricane with a little potted asparagus fern (I bunched some brown fabric around the pot since it was an ugly black plastic pot).
Here is a picture of the room from above and one of the buffet tables. I thought the little tables around the balcony with alternating brown and white tablecloths turned out really nice.
Because I had so many centerpieces to make and because I have another reception on Saturday (for another graduation ceremony) and need to use the same centerpieces (it's a budget issue), I had to find something that was quick, easy, cheap, and that would last a whole week. I'm watering the little ferns and will need to redo the 3 large flower arrangements, but other than that, these centerpieces fit the bill of fast, affordable, long-lasting centerpieces.