Let's say in checkers, I somehow manage to get seven pieces crowned. I only have twelve chips, but I would need fourteen chips to crown seven kings. What do I do? What if the opponent doesn't have enough non-playable chips to give me either?
(Warning: Clicking on the rulebook link below will download a Word document.)
From the American Checkers Federation's official rulebook (emphasis mine):
1.16 When a man reaches the farthest row forward (known as the “king-row” or “crown-head”) it becomes a king, and this completes the turn of play. The man can be crowned by either player ( ) by placing a man of the same colour on top of it before the next move is made. (It may be necessary to borrow from another set if no captured man is available for the purpose).
Like the rules say, if you run out of pieces, you can just borrow from another set. You are not limited by the number of pieces in your set.
If you are playing casually with friends, you can crown a king using coins, dice, torn pieces of paper, etc. As long as the board state is clear to you and your friends, it doesn't really matter how you crown your kings.
I've seen some checker sets that have different faces on the two sides with one side typically being a crown. I remember one silly game where this came up we just made sure all the crown sides were down on all the pieces then flipped the checker to mark a king. We only did this when there weren't enough captured pieces to make a king.