I like mushrooms in my omelette and sometimes with cheese steak. When I buy them and then use a few, no matter how I store them the rest turn into a disgusting goop. How should I store them?
Try putting them in a paper bag after you open them, it will help them last a little longer.
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I generally buy fresh mushrooms for whatever I’m doing that involves mushrooms, and then just pickle the rest for late night snacks.
I put them in a paper bag; they last for a number of days. May not be as effective as the method ginkgeng found, but it sure is easier. 
People who tramp the woods to harvest edible mushrooms, typically they build a “hot box” drying cabinet with trays and fan, so they can slice 'em up and totally dessicate them. That’s probably a bit too much work for store-bought mushrooms.
For commercially cultivated mushrooms, I wrap them in paper towel (so they stay dry and don’t touch each other, or the bag which is prone to condensation) Place the wrapped mushrooms in a ziplock bag. They easily last a week or two