Even if your "ordinary kitchen"'s pantry stocks both fluorine gas and liquid oxygen, I've some doubts about heating the former to 700 C (1300 F) in an kitchen pressure cooker. Especially the rubber-ish pressure seal. Then there's the lungs of the cook to consider, when fluorine gas "starts escaping through the safety valve".

(Yes, Randall's lawyer probably vetoed more-realistic escapades, due to https://en.wikipedia.org/wiki/Boston_Marathon_bombing But for the literal worst that could happen, he should have written about the chance of Vacuum Decay in the pressure cooker triggering the end of the universe.)