In the 1950's the English would talk of being 'financially embarrassed'. This describes it perfectly.
Ten pounds will usually get us home or get us fed in a crisis. It is better not to keep this in our wallets or purses as we are unlikely to have these if our cards are stolen. I have a bullet shaped capsule on my key ring which contains ten pounds. For some reason I forget I have the money- so I never spend it. I also keep small change for vending machines and so on in a second key ring dispenser.