Regarding the GI Poncho: Carried one for years stuffed in a cargo pocket. It's not a great way to carry the thing, but I can live with it. It's a very useful piece of gear. Though, looking at the prices on 'em online, it's not much more to get a high tech lighter one.
In basic training, we carried our ponchos tightly rolled secured to the back of our web belts with two blousing straps:
http://www.brigadeqm.com/cgi-bin/tame.exe/store/level4c.tam?xax=29626&pagenumber%2Eptx=1&M5COPY%2Ectx=21078&M5%2Ectx=21078&M2%5FDESC%2Ectx=Clothing%20Accessories&level3%2Ectx=level3c%2Etam&BC3%2Ectx=Clothing&BC4%2Ectx=Clothing%20Accessories&backto=%2Fstore%2Flevel3c%2Etam
Handy, compact and out of the way, I think you could to it with a normal belt.