Hi,
Yes you can. You can plug a Cisco USB Flash MEmory Module (64MB, 128MB, and 256MB) to store IOS Image or configuration file. Do not unplug the USB Module while read&write is in progress, your router will reload if you thus - it could also damage the module.
You can also use eToken Flash from Aladdin
http://www.cisco.com/en/US/products/ps6247/products_data_sheet0900aecd80232473.html
The difference is that the eToken is secure while the Cisco Flash Memory Module is not