Prosecutors from here to the coast will tell you that it's against the law to carry prescription medications in something other than the container in which they were supplied. If this were true, then everyone living in a retirement complex or assisted care facility would be guilty of possession of a dangerous drug.
The law in Texas states that "[a] person commits an offense if the person possesses a dangerous drug unless the person obtains the drug from a pharmacist... or practitioner..." A dangerous drug is defined as a drug "that is unsafe for self-medication" or is a drug that may only be dispensed with a prescription.
The law does not state that you cannot put your prescription medications in a different container. Where the confusion arises is with the offense of delivery or offer of delivery of dangerous drug. Delivering a dangerous drug to another is a criminal offense unless the drug was delivered by a pharmacist pursuant to a prescription and the drug is delivered in a container stating the name of the pharmacy, the date of the prescription, the name of the prescribing physician, the name of the patient and the directions for use.