I have seen ideas for these where you fill them with baubles or fairy lights, put a card over them, turn them upside down and decorate the stem or place a candle on the top, which is actually the base. Something like that.
For something more permanent, definitely put small plants in it, a dried flower arrangement or fresh flowers.
For a party drink, serve some punch or Pimms in it with a small ladle for decanting into smaller glasses.
At a party or barbecue, put ice cubes in it. Or crisps or sweets.
Maybe stand it decoratively in the bathroom with bath salts or cotton wool balls in it.
I'm sure people will pay a pound for it if it's not chipped or gone milky.