Do you stop at the Fan Store at the stadium, or do they sell them outside? And how much are they? I'm in uncovered seats, and don't feel like getting soaked to the core, but I still want to rep with Seahawks stuff...
layer 1- t-shirt
layer 2- Black garbage bag with head and arm holes removed
layer 3 - Jersey
I did this once out of necessity when heading directly from work to the game in an unexpected downpour with no raingear. It worked so damn well while keeping my hawks swag prominently displayed that I find no need for a poncho, hobo stylin yo!
Once you're in the stadium, find a guest services booth. They'll give you a free poncho with a Seahawks logo on the front and back. It's a really quality poncho too. My wife and I both got one during the SF game.
I'll be in my Milan rain gear, but they give away the ponchos I believe, that's what happened the last couple times there were chances of rain when I was there.