In the SCA period clothing is called garb. The only time garb is worn is at events i.e. you don't need it to go to meetings and most classes/workshops.

The SCA webpage states, "The only requirement to come to an event is that you make some attempt at pre-1600 costume." This is one thing I like about the group. In a 'living history' type group they could be super picky about what you wear. The SCA isn't like this. Ok, there may be some self-appointed authenticity police running around - put them in their place and ignore them. People will help you to learn more about the type of clothes your persona would wear or how they would speak but if that is not your focus then just make some reasonable attempt at dressing up and then have fun.

For example, I have a Medieval/Renaissance type shirt with buttons on it. The buttons aren't period but so what. Elastic isn't period and neither is most of the cloth that people make their costumes out of (most undergarments you would wear weren't period either ;-) ). I read that:
"Cotton was not grown in Europe until the 15th century and even then it was such a luxury fiber that even Queen Elizabeth herself only had ONE cotton undertunic (a gift from the Spanish court), and it was so priceless that she never even wore it!"
http://www.reconstructinghistory.com/beginners/FirstGarb.html
My point here is that don't let the fact that you don't have garb to wear prevent you from getting involved. Most groups have loner or free garb for newcomers. At one of the meetings I attended it was stated that the Barony of Cynnabar, the group that I am in, has boxes of stuff. There are lots of sites that show you how to make garb easily or you can buy it pretty cheaply either online, at events, or from people in the group that will hand-make you garb. Check out my SCA links page to find a bunch of resources.