The Three Jacks

This is a fairly simple trick which requires little or no preparation yet is very effective.

Method.

Firstly remove the four jacks from a full pack of cards ensuring that you place one jack face down on the top of the pack.  Start off the trick by showing the three jacks and making up a story about them being the best of friends and that they couldn’t stand to be separated and no matter what happened they would always end up together.  Continue to make up a story about how they are lost and have to separate to go and find help and so they disappear in different directions.
At this point, get the volunteer to place one jack on top of the pack, one jack on the bottom of the pack and the remaining jack in the middle of the pack.  Add some theatricals by asking your volunteer that he is happy that all of the jacks are well separated.
Then ask him to cut the pack and put the bottom half of the pack on top of the remainder.
As you will have probably worked out, this now brings the top and bottom jack together with the previously placed jack on top of the pack.
Ask your volunteer to pickup the deck and start turning over the cards, you can add a commentary as to how they are going to come together shortly, and eventually your volunteer will come to the point in the deck where all three jacks are together.
The main part of the trick is ensuring that you do a small amount of misdirection at the very beginning as you select the  four jacks and do not make it evidently apparent that you are placing one jack on top of the pack.
It is a very simple trick and one which, once learned, you will not forget easily and you can do any place at any time to amaze your audience.