For MS contin and most other long acting medications, the withdrawal will start between 8-12 hours after your last dose, and "worsen" a bit as the hours go by. The things that Susie gave you will help manage most of the symptoms of withdrawal and coke syrup that you can buy in most pharmacies will help with nausea, along with the crackers. Hot showers and baths help with the sweating and chills- immodium for any diarrehea.
Fentanyl, butrans, methadone withdrawal may take a day or more to start before you start feeling the symptoms simply because of the method of delivery- with the patches, the meds are absorbed through the skin and it can take 12 hours or more before your blood plasma levels start to fall low enough that you are starting to experience withdrawal symptoms...Methadone because of it's long half life- can be a few days before you start to experience symptoms, and may last a bit longer than the withdrawal symptoms for other meds such as the others we were talking about.
I would stay away from xanax or valium , they aren't necessary to manage withdrawal symptoms and might get you into trouble for taking them when they aren't prescribed by your pain management doctor, should he decide to have you do a urine test...I would also call their office and make sure that they know that you are completely out of meds, due to the storm and that way, if they do pull your name for a urine screen, it should be no surprise if your levels are negative for the meds...
Don't substitute another medication for your prescribed meds, because again, doing so can get you dismissed and it's not worth jeapordizing your treatment with this doctor .
Good luck