If you're reserve, you'll probably get it a few days prior to the start of your basic training. Reg force you go in civvies and you'll get your uniform in the first few days, IIRC, we got ours on the second day. Until you get the uniforms, you'll be in civvies. Don't worry, everybody will be the same and you're not diggin trenches the first week. It's mostly administration the first couple days, things like pay, travel claims, getting your uniforms, learning how to make your bed, etc, and a lot of standing around since there's a ton of recruits/Ocdts and only a handful of clerks doing your paper work. Don't sweat it, they know you're a Joe Civvie, that's what basic is for, the basics.
Cheers