If you used panda's USB vaccine to disable autoruns from flash drives, and used a portable AV such as Dr Web's CureIt, and throw in Virus Total's upload right-click extension, you'll be fine. Add a ton of common sense though. But, some will argue, the trouble going to update, and ensuring you scan every unknown file run, versus just doing what you got to do and have a realtime AV protecting you at all times, most will choose the latter.