Lots of great information in this thread! Boggart also makes great lightweight track only wheels to help with weight reduction. I do beleive my 13x8 flystar wheels are 7lbs per wheel. Add a set of Bias Ply Street Slicks or slicks and you have a very light combination. My 205/60R13(~23"X~8") M&H Street Slicks Only weigh 15lbs. Even the 15x8 models don't weigh that much more.
For most street cars that run at the track, I usually tell them to gut the trunk completely down to the bare metal and use the smallest diameter wheel combination they own if they don't have dedicated tire/wheel combo.
1998 Ford Escort ZX2
Full Bolt-On's, SCT VCT Tuned ECU, 3500rpm Edge Racing Stall, 205/60R13 M&H D.O.T Street Slicks