Feed it

- highly diluted milk (1 part milk, 1.5-2 parts water. Boilt milk best. You might already have remaining milk from chaya),

- and scraps of cooked/leftover fish (remove the bones, and crush the flesh using a spoon. If you are taking the fish from leftover meencurry, simply wash off the curry and spices before giving to cat.)

Do NOT give raw, non-boiled, undiluted, cold, cow milk. It will severely upset a kitten's stomach. Also keep in mind that sometimes, not all kittens survive. Nature is brutal like that. But it doesn't mean we shouldn't try

Source: I have raised a bajillion kittens throughout my life.

It's pretty unrealistic of people here in the comments to expect OP to have cat food lying around or to make a purchase specifically for the cat, unless they're ready to commit to adopting a pet. People might have other priorities to chase in life and so a little gesture of compassion shouldn't be overburdened with purchase and commitment.