For some reason, stores tend to package mushrooms in little boxes wrapped in plastic cling film. Presumably, this is to allow customers to see the mushrooms, while also … I dunno … preventing them from escaping? Whatever the reason, the cling film is terrible for the environment, and just as bad for your mushrooms.
Like pretty much every vegetable–in fact, this bit of advice is applicable for all your produce, really–mushrooms spoil faster when they’re wet. Keeping them wrapped in plastic traps moisture in with them. This is especially bad with cling film, since it actually presses the moisture against the surface of the mushrooms, making them susceptible to spoilage much faster.
Your best bet is to pull off the cling film and throw it away as soon as you get home. If you’re going to be using the mushrooms slowly, or not right way, you can dump all the mushroom out of their box, place a folded paper towel across the bottom of the box, then dump the mushrooms back in. This will wick away moisture and keep them dry, which will extend their shelf life for a few more days.
EAT IT!