What does not make sense is that a tow company can set their price, and retain not only the vehicle, but everything in the vehicle to satisfy their charges. I realize that in your situation you merely wanted a pair of shoes out of the vehicle, however if they can keep your shoes, they could keep an item worth far more. Somehow I do not think this thinking would hold up in court. I believe I would research and see if they are really within their rights to retain personal property in the vehicle, then if you find they are not, I would make it a point to enlighten the tow company and probably local law enforcement that may be involved.
Here is one excerpt from a legal document in one state (no idea where, but this is just common sense to me). There is an old saying "possession is 9/10ths of the law", so it is a tough situation, but I doubt they have legal right to hold personal possessions inside the vehicle. But lesson learned to be careful who tows your vehicle, and where it goes, and make sure to clean it out before letting it away.
"(b) No lien shall attach to any personal property in or on the
vehicle. The personal property in or on the vehicle shall be given to
the current registered owner or the owner's authorized agent upon
demand and without charge during normal business hours."