The drag and drop behavior has a property call "Axes". Set it to Horizontal Only.
[Edit] I realized I made an assumption when I wrote this. I assumed you knew where the properties for behaviors were. If you do already know, you don't need to read any further.
If not, I'm sorry. I should have been more clear. This is how you get to the properties for behaviors. The entire left of the screen is a menu called Properties. Select the Bread object in the objects menu on the right of the screen and the Properties panel on the left will show properties for the sprite. If look through those, you will find the Behaviors group and inside is the DragDrop behavior.