My simple set up:

• One $20 bill
• Two $10 bills
• Two $5 bills
• Five $1 bills

Few places take 50s or 100s.

So starting with $20, each lower denomination adds up to the previous - two 10s makes $20, two 5s make $10, five 1s make $5.

The goal: easily cover any cash-only costs (or tips)

You could add more, but I don't like making my wallet bulkier than it needs to be.

At home, I'd recommend having $1,000+ cash on hand for emergencies.