Best offline resource for mushroom identification?

I've recently realized I really enjoy searching for mushrooms on hikes. Been doing it for a few weeks now and have seen dozens of different kinds of mushrooms, it's been amazing! But a lot of the areas I'm in have no cell reception and am not able to upload photos to inaturalist for identification. Is there an offline app or should get some books on mushroom identification? Also is inaturalist the best app for online identification, and is a topside and underside image enough for an accurate identification?