Hopefully its not as bad as just literally 0 SNAP benefits get sent out, there are a number of last resort contingency plans and funds that could be used… but it wouldn’t be very much, and they’d run out fast.
I have zero doubt that the trump administration would direct agencies to not use any last resort contingency plans (if they exist), just so people suffer from this. Remember why we're in shutdown anyway: because trump and the GOP took away healthcare from poor people. Now taking away food is entirely on-brand for trump and the GOP.