be pot luck

be pot luck

To be a casual meal in which nothing has been prepared in advance. (A potluck, when spelled as one word, is a shared meal in which separate dishes are prepared and/or brought by different individuals.) Primarily heard in US. I hope you can join us for dinner on Saturday—it'll be pot luck, so just bring something that we can all share!
See also: luck, pot
Farlex Dictionary of Idioms.

be pot luck

If you ask someone to have a meal at your house and you tell them it will be pot luck, you mean that you have not planned it or prepared any special food. Note: `Pot luck' is usually written as `potluck' in American English. `We'll just be casual and eat in the kitchen. It's just pot luck,' Moira said. `Hope you don't mind.' Note: A potluck is a meal at which different guests bring different parts of the meal.
See also: luck, pot
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • potluck
  • put the cat among the pigeons
  • put the cat amongst the pigeons
  • put/set the cat among the pigeons
  • set the cat among the pigeons
  • go walkabout
  • rock up
  • nothing to complain about
  • chitchat
  • have a knee-trembler