When you are first brought in before security, you are best advised to request an attorney and not answer questions. Any attempts to explain yourself may be used against you and might undermine any defense you might later wish to present.
Once at court, an experienced attorney can help you weigh your options. Maybe you were extremely stressed and really did forget you had the DVDs in your cart. Maybe the evidence against you is weak. An attorney can help determine whether you should take the case to trial.
But what if you really meant to take the DVDs? If the evidence against you is too strong to risk a trial, you may still have options. There may be alternatives to a conviction such as attending a special school. Your attorney might help work out a plea agreement. For example in Illinois, you might be able to take “supervision,” which is technically not a conviction. Then, if you meet certain requirements, you might be able to expunge your arrest five years after a successfully discharged supervision.