How do I mount a USB device / USB stick
Run 'mount /mnt/external1' for example if you want to mount /dev/sda1. udev on grml does multiplexing for USB block devices, /dev/external1 is a symlink to /dev/sda1.
boot grml via USB
It is possible to boot grml via USB (e.g. USB stick or harddisk), firewire, or running from a Compact Flash disk. It works out of the box; you don't need to modify anything. If accessing the device fails, use the 'scandelay' cheatcode on bootprompt. So, boot with 'grml scandelay'. If the timeout is still not long enough add the time to wait in seconds as parameter: 'grml scandelay=15'. See usb-webpage in the grml-wiki for more details.