You regular medicines like blood pressure meds are fine. If you take meds for diabetes you should check with your Dr. because you wouldn't want your sugar to drop too low. Most of your other meds could simply wait til after the test which is usually first thing in the morning anyway.
You can continue to taking prescription medicines unless directed not to by the physician ordering the blood sugar test. However, vitamins and supplements are strongly discouraged because some of them, like Vitamin C, are a frequent culprit in erroneous blood tests.