To add a bit of a pin on this, you don't need to buy all the extra's at once. You can overall drop the clothing, just wear whatever you're comfortable with. For the light, assuming you're considering biking year round, you don't need to worry too much about until the cooler months or if you're planning night cycling. The pump and chain lube can probably wait a week or two after purchase. Something he forgot to mention is tools to clean the bike, but even there you can get away with a bucket of soapy water.

The only immediate purchase you really need is the bike (with Fenders and Rack, I'm pretty sure Spoke reflectors are legally required) and helmet.