Before getting the Anova we had bought those prepackaged salmons from Sam’s Club, the ones already marinated. My question is whether there is any reason I cannot just use those packages? Is there some reason why I should remove the salmon and put them in zip lock bags? The instructions on the box, unsurprisingly, do not include how to cook sous vide.
I would totally do that.
What a great idea, marinated salmon already vacuum sealed ready for us to give it a hot bath 
I wonder if they have it at Costco, I’m not a Sam’s Club member.
If there is a paper label on the package, pieces of paper can come off and get in the impeller. I would repackage, although another solution is double bagging.
Yet another solution is a short soak in a cold water bath to remove the label before you put it in your SV setup.
Does the packaging doesn’t indicate if it’s made for cooking temps?
If not, I’d monitor it the first time (just in case it begins to leak).
Just double bag it.
i have used those several times with no problem.