Objects in Exporting Package window cannot be multiselected (with Shift+Click, Control+Click) in order to include/exclude them from the final exported package. (We have this functionality in the Build settings when deciding which scenes to include in a build, it makes sense we should have it here, too).

Real world use case: I was trying to create a smaller repro project for an issue. I selected Export Package from the right click menu on a huge scene file. In the Export Package window, I wanted to deselect lots of different groups of assets here and there, so that they are not included in the final exported package. The only way to do that right now is to deselect assets one at a time (painful!)