MacBook Pro and Thunderbolt Display
Obviously you need a computer, but not just any computer. You need a MacBook Pro with a retina display and a Thunderbolt display. If I’m traveling or just get sick of working from my home office, I want to quickly grab my computer and work on the go. Having a MacBook Pro with a Thunderbolt display makes it easy.
A Local Server
I personally use MAMP Pro as my local development server. I have trouble focusing on more than one project at a time — ADHD and all. However, if you work with multiple clients, Desktop Server may be perfect for you.
I spend a lot of time editing code, so I need good development software. I personally use Espresso, and I love it! I’m told Coda is just as good or better, but slightly more expensive. If you’re using archaic software like Dreamweaver — stop. Invest in one of these apps, and don’t look back.
A Starter Theme
Using a good starter theme will get you 90% of the way there. I initially created the Seed Theme to be a starter theme for my development process. However, it had some limitations. As a result, I ended up creating a new starter theme — the Swell Theme. I released a free version available on Github, and a premium version available from Organic Themes. The recent update to my site was built using the premium version of the Swell Theme.
No theme developer should be working without the Developer plugin. This plugin contains a number of essential development plugins including Theme Check, Regenerate Thumbnails, RTL Tester, Debug Bar, Beta Tester and more.
Firebug or Equivalent Inspector
I’ll probably catch some flak about this, but I still use Firefox as my primary browser. Firebug is an essential tool for my design and development process. The Chrome inspector is equally as good, if not better. Regardless, use an inspector, and use it frequently. You can practically learn web development just from playing around with a good inspector.