Hi! Well, for xmas i do something like that as gift for my customers. I prepare a usb with many tiny linux distro bootable via usb and with grub (to choice the preferred distro).
There are a lot of minimal linux distro, and many are debian based (DamnSmallLinux, Knoppix, for example). I think that for your aim you must use a live distro. It's quite easy to use a live distro in a usb device. You can : - format usb devices as fat: # mkfs.vfat -n <volumename> -F 16 <usbdevice_partition (/dev/sda1, for example)> - mount the live cd iso and usb device: # mount -o loop <iso> <mount point> # mount -t vfat <usbdevice_partition> <usbdevice_partition_mountpoint> - copy all content to usb device. # cp -a <iso mount point>/* <usbdevice_partition_mountpoint> -if it's a livecd, probably use syslinux/isolinux to boot, so find syslinux.bin and syslinux.cfg (in root directory) OR isolinux.bin and isolinux.cfg (in /boot directory); if you find isolinux.* in /boot directory, copy those files in root directory, renaming those in syslinux.*: # cd <usbdevice_partition_mountpoint> # cp boot/isolinux.bin syslinux.bin # cp boot/isolinux.cfg syslinux.cfg (you can modifiy syslinux.cfg to change default boot delay, background, font or to add another distro) - umount usb device: # cd # umount <usbdevice_partition> - and make it bootable with syslinux: # syslinux <usbdevice_partition, /dev/sda1 for example> Hope it helps you!