The N-Rage way worked for me, you probably just had to change mpk to n64 in the file browser, it's a dropdown.
This might be easier though. It's a mempak/dexdrive reader. Not exactly user friendly but it works. Drag over the .n64 file and open the JS console (Ctrl + Shift + K), and type in extract(0). It'll save the contents as a file and you rename that to whatever your ROM is named. [Old pic]
EDIT: Improved version of the tool above. It's a full-fledged controller pak viewer/editor.
Though for extracting SRAM/EEPROM saves, you'll have to strip off the first 32 bytes of the exported notes, to work in emulators etc.