I have been using ubuntu live OS everyday as my internal hard drive has gone for replacement. On every boot up i need to create a DSL connection to connect to the internet which is a mundane task. I need to write a bash script for the same.
You would have to store any script that you create. Storing it on a flash drive would be easiest to store it on.
But if your going to use a flash disk, you could just use a 4 gig (minimum) or greater USB flash disk to install Ubuntu on it pretty much the same as if you were installing it Ubuntu to the hard drive. That way every custom setting or additional installed software will remain the same after reboots.
After establishing your connection then in a terminal it would be good to run "sudo apt-get update" ; then run "sudo apt-get upgrade". Remember all changes and upgrades will remain.