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I flew qantas and took formula in one of those things that holds three feeds of formula and water in bottles. It's was fine, but check with the airline. I'm sure you could take a tin of formula in your suitcase, just either get a new tin or tape the lid on.
Make up the bottles you need for the flight. Pack your tin in your case. We flew interstate (WA to vic, WA to NSW, WA to QLD) when our eldest was a baby and this is what we did. No issues.