In 2.7, we had a button to show all the layers. In 2.8, this button is for the Pie menu. Do we still have this functionality for Collections?
In Blender 2.8 you can isolate and iterate on each one by pressing the numbers on your keyboard, this will show only the collection that you want and hide the others, if you press Ctrl + H it will give you the same result. To show all the collection again press Alt + H.
Go the the outliner. Ensure the "Viewport Visibility" eyeball icon toggle is active.
Pick any collection in the outliner.
[CTRL]+[LMB] once on the eye to show only it.
[CTRL]+[LMB] again to show all collections.