I recall the first few digits of π, 3.141592653, with the phrase "May I have a large container of sweets right now". (Other π mnemonics are available.)
However, it's probably not surprising that I have not needed to use this knowledge in my daily life. Indeed, 3 is a relatively good estimate of π, as seen in the pie chart to the right.
If I really do need more accuracy then the simple equation of 22 ÷ 7 is a great estimate which is within half a percentage point of the exact figure. It's so close that the difference doesn't even show on this chart.