I have the same need. latextools may not be fully developed yet. At least the autocompletion part is not completely done compared to the one I used. (I had been using AUCTeX in Emacs.)
For now, you may reduce your typing by using ctrl+l, e command for creating environments.
type the name of an environment, such as 'enumerate', and then type ctrl+l, e. That should complete the block.
