I think it would be a nice addition to have a mushroom picker bag in which one could store mushrooms. Similar to a dry goods bag, but it would be only for mushrooms, holding maybe 8-10 of one type (i.e. different bag needed for each type of mushroom). It could be made to take up like 4 inventory slots, so the advantage isn't quite as big. But for more advanced characters and towns, it would be a nice way to level the ratio between the need for mushrooms and one's inventory capacity, without introducing something like traveler's sacks. It should require mid to high-tier goods for its construction, and have a fairly high price in Boston shops.
It's inherent in my name to suggest something like this...