When to buy baby things and what to buy?

I am 13 weeks 1 day pregnant with my first. I had my first scan at 10w5d and I heard the heartbeat and everything was fine. I am having my second scan in a few weeks and my dr said he could tell me the gender then. He does a scan at every visit with everyone of his patients. I am just wondering when should I start buying things and what I need to buy. We are going to try to spread everything out and buy clothes last but we don't know everything we need to buy and when to start. I am so nervous and excited :) So any help would be appreciated. Thank you so much.