I'm looking at a picture of one made of rootbeer barrels. It looks like they use a glass sundae cup and put a few candies in the bottom. They stuck a round styrofoam ball in the top of the cup and pinned the candy to the ball with maybe straight pins or hair pins.

I'm attaching a link for candy centerpieces. You can probably figure it out from this.

Here is a link that might be useful: candy centerpieces

Thanks! Kim