You need to find these hotdog stands in Act 1, and shoot them.
Act 1-1: Just beside Bumblebee when the second part of the mission commences. You'll see the stand in the cut-scene.
Act 1-2: Last part of the mission, you need to reach Grimlock. The stand is all the way at the end of the level, behind Grimlock.
Act 1-3: When you fight Soundwave - at the beginning of the battle, the stand is near an enemy bot on the right.
Act 1-4: At the beginning of the mission, the stand is found at the left of the Autobots.