A native file browser for USB flash drives will be included in the next version of Android (codename M).
A lot of Android devices can recognize a flash drive, but up until now you’ve needed to use a 3rd-party app to explore an USB flash drive.
When you insert a USB flash drive, a USB icon will show up in the notification area asking if you would like to explore or eject the drive.
A list or grid views can be viewed. Both views will show thumbnail icons for photos and other types of content. When open the settings view you can see information about the amount of available space as well as options for ejecting, or erasing and last but not least formatting your flash drive.
Look here at the video below for a demonstration (thanks to Brad Linder from Liliputing)