Assuming you are caught, you would be tried by a local official. While there was a grand court in Tenochtitlan called the "Teccalco" which tried for treason, you would have been sentenced by a warrior, which is to say a local noble. This holds true throughout the empire. Local authorities always took care of petty crimes and even many major crimes. This noble could do with you what he pleased, so here's two examples of what he might do.

1. He would demand you paid for the food you stole. When you told him you had no goods to barter with, he could make you a slave of the man you stole from. Or his slave. Basically, you would lose your autonomy but not your life. You could probably earn your way out of this and become a farmer eventually if you were lucky in masters and dutiful.

2. The noble would have you killed immediately. This was a common reaction to even minor crimes within the empire and could take the form of sacrifice, strangulation or stoning. This is due in large part to the fact that the Aztec were very recently nomadic. They had no prisons built and no concept of a prison system. Their religion also demanded a great deal of blood to satiate their gods and forestall the apocalypse, which meant that they had little reason to imprison a perfectly good morsel for these deities.

Hope that answers some of your question. Glad you posted it because it got me looking back over stuff I haven't read since I was in college.

Did someone see you doing this? That's all the difference.