Sit down to any demo box in an Apple Retail Store (or any Leopard system) and have Git, RubyGems 1.3.1 and SQLite3 working for you in less than a minute.
Paste the following into Terminal.app on any Mac:
mkdir -p work && cd work curl http://github.com/JackDanger/apple_store/raw/master/install.sh > install /bin/bash ./install
Then, when you're ready to leave:
cd .. && rm -rf work
And it's like you were never there.
You can work at the Apple Store. Or on your wife's/husband's computer. Or on a school computer. You don't need root access or XCode installed to get yourself going.
It doesn't install any files outside of the current directory. You can delete the folder you installed it from and the system will revert to it's previous, boring, condition.