By situation

Only 30 minutes

Pick one thing. Eat it standing. Leave.

Thirty minutes is enough for one item at a counter or stall: a tamagoyaki on a stick, a few pieces of sushi at a standing bar, a cup of uni. It is not enough for a sit-down seafood bowl with a queue.

Use the I'm in Tsukiji Now button with 'Just a bite' and '15 min'. It only shows shops open right now.