A prime lens (35mm for APS-C or 50mm for FF).
Don't spend money on tripods, flashes, bags, etc., until who've reached the stage where it is a necessity. Also, use this non-purchasing time to save-up your dinero for buying the best available, and not simply the best you can afford (now). By the way, for a bag I personally use those "six-pack" cooler bags and wrap everything in lots of (genuine) flannel.
As for software, Canon's DPP is sufficient (and free!), again until you're actually pushing it to the limit.