How do I create a bootable snapshot image of Lion?

How do I create a bootable snapshot image of Lion? In the past, I used disk utilities - restore to create a copy of current hard drive on an external drive. If there was a problem, kids could boot to external and work until internal drive was fixed. This proved to be a great solution. On a new Macbook Pro with Lion, I get an error when I try. It says to do a restore from the recovery disk, but the recovery disk says it is a limited function OSX. I would like a full OSX so they can continue to work and even copy files over if the internal disk is suffering intermittent failures enough not to boot but not enough to keep from copying files. A few years ago one of the kids had a disk/boot failure duing finals but was able to boot from the external hard drive, copy over what he needed and access the internet so that he could finish the exams. Time machine is great, but there are instances where you need a quick fix to keep going until the new hard drive arrives.