If you get hit with two weapons (as in the opponet is using two weapons or even multiple attacks) - the damage is resolved at the same time.
Bad example. you can resolve each attack, even simultaneous ones, in a set order, so that if you drop a foe with your right sword, the left can attack a still living target.
As for all the people saying poison takes time to work, not really in game. Maybe in reality, but no the game. And death attacks aren't necessarily immediate, in real life or in game. I remember a scene from some Jet Li movie where he finished off the villain with a death touch that slowly killed him while leaving him helpless and bleeding through the eyes and nose for a full minute. For an in game example, there's the Monk's class feature.
Since damage tends to come before special effects, and poison is both a form of damage and a special attack, I'd rule weapon damage, poison (initial), death attack, in that order. And as usual, no weapon damage means the other two never happen (well, assuming injury poison and not contact).
EDIT: For the record, I'd pretty much follow that method and make it standardized. If a druid found some way to get the Wounding property on her wolf companion's teeth, for example, I would say it happens in the order of: bite damage, con damage, trip attack. It wouldn't particularly matter in that case unless the con damage killed it before the trip, of course. It would if it was a dex or str poison instead of Wounding.
