Pro tip that I saw somewhere and have successfully executed with a couple random lobbies: if the extraction site is relatively convenient, dump your samples there. That way if you all do make it to extract, the samples are waiting for you, no one is out running around with them. If you don’t make it, no major loss.
Exactly! For a sweaty gamer note: completing the last objective vastly ramps up the number of enemy patrols by almost 4x. Also sitting on the extract point causes more patrols to spawn, as does splitting up into separate groups.
So the absolute worst thing you can do to farm samples is complete the objectives, then have someone wait at extract while someone else goes and farms more samples. If you want to easily farm samples, save the last objective until after you've gathered your samples!