Think right now, how much cash do you have on your person and at home, and now divide that by your total assets. How high is that percentage? Generally, the percentage is around 3% of the total money is held in physical form.
Credit cards and debit cards have driven down the size of the physical currency due to their ease of transactional use. Furthermore, as more purchases have moved online credit and debit (and Paypal or Stripe) have pushed down the need for physical money.