User chooses items that display on next slide

I asked also 'where do they have to be displayed', in case you wanted them in the same location as on the previous slide. But since you talk about dragging, that seems not to be the case.

You'll have to put all those 'items' on the second slide, and hide them for output (top of the Properties panel if I remember well). Give them a identifying name.

If you use the click approach, create a standard advanced action (I would use a shared action):

  Show Image _x                 where Image_x is the item you want to show on the next slide; for a shared action the image will be a parameter

It is necessary to do this by a standard action because a simple action will release the playhead. See: Why choose Standard over Simple action? - Captivate blog

If you use the drag approach, you'll also need that action that you will apply as Object action for each drag action. Have a look at:

Drag&Drop tips - Captivate blog