Am I sinful for having an unknown piece of cloth and unknown medications in a bus I sold, given that I forgot the medications in it and neglected them? And what should I do about it?

The cloth found in the car is considered a lost item (Luqatah). If it is insignificant, such that its owner would not bother to search for it, then there is no harm in benefiting from it directly. However, if it is valuable and its owner would search for it, then it must be announced for a period of one year. If the owner is not found, it may be utilized, becoming a trust with the person who found it, and must be returned to its owner if he appears. If the finder gives it away in charity and the owner later appears, the owner is given the choice to either approve the charity, or take a similar item, or its value. As for the medicine, it is usually something that its owner would not meticulously search for, and it is prone to spoilage quickly, so there is no harm in utilizing it.