I don't keep cash in my BOB, but would not "bug out" without my wallet.
My wallet has (at minimum) $100 in it at all times. I usually have more cash.
In a short term emergency, the more cash you have the better.
In a TEOTWAWKI situation, cash (paper money) = worthless.
Didn't a cord of firewood cost $8,000,000,000 Marks during the 1920's German depression?