In Malayalam/Indian, there's a saying "Aana vayil ambazhanga", which literally translates to:

A small fruit in an elephant's mouth.

It means:

Having too small an amount for a very large need.

What's an equivalent idiom in English?

"Bring a knife to a gunfight", can mean entering a conflict without preparation. "Too little, too late" can mean something is not in time to be effective. These don't fit here, because I want it to only mean "too small an amount for a very large need" and nothing more.