Strike: The one VI I love to hate and hate that I love it.
The blue keys to the right are the assignable ones, as was mentioned. If your kit does not have the specific instrument in it, you have to add it. The way I figured out how to do it was to have the kit window open and scroll to the channel where you want to place the instrument. (the 1 thru 12 spaces on the right hand side.)
Next, go into the kits on the left hand side menu list. It's like one or two options down from presets. You'll have to go through the kits and expand them to show the instruments. I think you can audition the instrument somwhow, but I don't remember 100% for sure.
Once you've found the instrument - in your case the shaker(?) you mentioned - you simply drag it over to the channel (1 thru 12 on right side). The instrument will be ready for you. Now is when you do the right-click on the blue key that you wish to trigger the hit. A huge right-click menu will appear full of all of the instruments in your kit and their varieties of possible hit types. Select the one you want.
From there, you're back in familiar MIDI land. If you're not on the blue keys range, you'll simply have to transpose or drag the note(s) down to the blue range. In the future, I'm going to load all the hits I want to use down to that blue key range so that I don't have to keep scrolling up and down in the MIDI edit window. But, that's an aside and shows you how slow some things hit me.
I hope this helped.