PCManFM
PCManFM is a free file manager application and the standard file manager of LXDE.
Installation
Install the pcmanfm package.
Additional features
Add lxmenu-data to be offered a list of "Installed applications" when opening a file.
Add shared-mime-info to recognise different file types.
USB Automounting
For USB mounting support, add the following line to your configuration:
services.gvfs.enable = true;
If automounting still does not work you may need to explicitly enable devmon and udisks2. Keep in mind that all removable media will automatically mounted even without pcmanfm running.
configuration.nix
services.udisks2.enable = true;
services.devmon.enable = true;
SAMBA mount support
Configuration can be found under the Samba wiki page.