I am wrapping up simulation and testing of a new component called "Veelite." It means: Virtual EEPROM Lite, and it is a library integrated into OpenTag that now performs file management for UDB, RDB, and other Mode 2 data elements. It is designed to run well on NAND Flash (with wear leveling), but it is stratified in order to easily migrate to future non-volatile memory systems such as FRAM.
It's hard to say exactly, but Veelite appears to compile into about 6KB, INCLUDING the data heap that takes 4.5KB in the stock configuration. Static SRAM usage is less than 64bytes, and max stack usage is very low as well. It other words, Veelite is much lighter weight than Contiki's Coffee FS, although Coffee is very good if you want more features. Down the road I would like to have Coffee as an option for OpenTag, as well. Maybe someone from the community will make it happen before I do. :)