After you scoop out some ice cream from the tub and put it back in the freezer, it's common for a layer of ice crystals to form top. The easy way to avoid that is to use baking paper to protect it.
As AO Life notes, it isn't going to entirely stop ice crystals over several days of non-usage. But it should slow down the formation sufficiently till you reach in for another scoop. Another advantage of this method is that it also stops the ice cream from absorbing freezer odours, says Epicurious.
This is also a neat way to reuse the scrap paper that you may have cut out for your baking. No need to throw it away the next time!
AO Hacks: Tips For Your Freezer [AO Life]