(from) hand to mouth
With just the bare minimum of money, food, or resources to survive, with little or nothing else to spare. Usually preceded by "live." It's been pretty hand to mouth these days. If I don't find work soon, I don't know how we'll get by. With another child on the way, it looks like we'll be living from hand to mouth for the foreseeable future.
hand to mouth, from
With only the bare essentials, existing precariously. For example, After she lost her job she was living from hand to mouth. This expression alludes to eating immediately whatever is at hand. [c. 1500]