Nearly all aircraft have supplemental oxygen canisters on board, they're for the crew or in case of passenger medical requirements, not to supplement the pax oxy generators.
There are a number of items needed on board aircraft which have potential use as a weapon, fortunately the main threats aircrew around the world face daily are not terrorists (despite what the media would have you believe) but good, old-fashioned medical emergencies, technical malfunctions, disruptive passengers and the threat that we may make a mistake in operating the aircraft.
So some bits of equipment are rather important, whether or not a paranoid Daily Mail reader may consider them a threat.