I'm doing plenty of other things too:
Xorg.conf:
Option "DontVTSwitch" "true"
Option "DontZap" "true"
inittab:
tty1::once:/sbin/getty -nl /sbin/autologin 38400 tty1
::ctrlaltdel:/bin/true
.profile
nohup startx >/dev/null 2>&1 &
.xsession:
$(grep -q nosuders /proc/cmdline) && sudo sed -i -e 's/^tc/#tc/' /etc/sudoers
There is no window manager loaded, and Xprogs.tcz isn't loaded either. Because getty runs once, startx keeps running after the shell exits, the three-finger salute is disabled, VT switching is disabled, X zapping is disabled, and su is disabled getting to a session with privs will be hard. Oh, and there's no keyboard either, just a touchscreen.
Making it read only is just part of locking it down. I like the chattr idea, but this is a FAT32 file system so it's not an option for this project.
Andy