Gear

Depends on the projects and how many you are going to get involved in. Normally you need to test stuff on various operating systems (Windows, MacOS, Linux). The main reason from a translation point of view is because they all use different default fonts, each with their own width issues. Say you're doing Firefox and working off a Windows machine. It'll very likely look great on Windows but if you test it on Linux, you'll find that lots of text runs outside the windows and you need to adjust width settings.

So even if you don't have all the hardware around, it's a good idea to have some friends who have hardware you don't have so you can ask them to test stuff.