My old team, 11, has a very recognizable presence at our events because of our competition uniforms. What we have done as a tradition is wear our yearly t-shirts, sweatshirts/hoodies on Thursday and sometimes Friday, and then wear our Pit Crew uniforms on Saturday. It allows us to have new and different t-shirts in each student's collection but then on Saturday we are all one big unit. The uniforms are purchased freshman year and last all 4 years (at 40 bucks a pop) and then t-shirts are cheap.
Some of the t-shirts are "I <3 Autonomous Mode", regular MORT t-shirts, and new for the year are shirts related to the team's pumpkin chunkin contests.
You can see all the different apparel in these pictures
http://mort11.org/photos/2011mortrollout
Most teams share this concept as well. We'll most likely do something similar on 3929- have a dedicated uniform for competitions and major events, and then have other t-shirts and hoodies that can change year to year or whenever someone comes up with a cool design. (I personally love 2056's polo's).
Hope that helps.