Standing at corner of Lichfield St and Colombo St, you have a selection of stores at your fingertips practically in all directions:
Bivouac/Outdoors, Kathmandu, The Great Outdoors, High Country, Snow Gum, Footrunner
What to buy: Anything outdoor. Not that I'm much of an experienced outdoor person, but judging from these stores, the stores mostly sell really good brands, and they know give good advice. No extreme sales pitches, but down-to-earth recommendations.
What to pay: Depends on what you're looking for, but quality outdoor gear does not come cheap.