What adaptation would be beneficial for mammals living in either a desert or in a taiga biome

Fat in a hump.

It would hydrate you

Things that I can think of off the top of my head are things like being able to store lots of water (like camels), light colored skin or fur so that they can't blend in to the surroundings and not get too hot, little to no hair or fur, and feet that can withstand the hotness of the sand.