If you are recording in Training mode then by default Captivate should include click boxes in your slides. You can assign keyboard shortcuts to those click boxes by carrying out the following steps:
1. Double-click on one of your Click Boxes.
2. In the Click Box section of the dialog box click the Select Keys... button.
3. Select the option Attach a shortcut
4. To perform an Undo choose Ctrl and then from the Letter menu choose
Note: To get the learner to Shift + Click, select the option SHIFT
5. Click OK to Close the Shortkey dialog box.
To simulate an Undo you would then need to branch to a slide where the original action was performed. Here you can either use the On success options Go to Previous Slide or Jump to Slide and then specify the slide number.
As for simulating selecting multiple items, again you would carry out similar steps. Depending on how your project has been setup you would either set the On success action to Continue or to Go to next slide.
The way I tend to work is that I have each of items I want to select on separate slides and then add a click box with the keyboard shortcut Shift attached. When the learner clicks on the first click box I then move to the next slide and so on. Naturally, this does not account for allowing the learner to randomly select the items. To accomplish that, you would need to set up some pretty complex branching.
Best - Mark