I know absolutely nothing about babies, but I know a little bit more after reading a report in the NYT about the baby formula shortage in the US.
Babies basically need breast milk or formula until they can start to eat solid food (at 6 months).
Do not dilute formula.
Do not try to make your own formula.
If you are out of options, give your baby pasteurized whole cow’s milk for a brief period of time.
Get advice from a pediatrician if your baby needs a special formula that has become unavailable.
One can will last 6-7 days for a newborn, and maybe as little as 2-3 days for a 6-month old baby.