Shelf life of cooking wine and would you blend it?

I know this is 2 questions but didn't want to start 2 threads since it's on the same topic. Lately since my wife has not been drinking wine we always have much more left over and sometimes accumulate 2 or 3 partial bottles and she'll use it for cooking. Assuming it's in the refrigerator how long would you keep wine you're going to cook with before you pour it out? A few days, a week, more?

Also if you have more than one red and/or white would you consolidate it in one bottle if they are not the same varietal? Now I'm not suggesting something crazy like blending a Cabernet Sauvignon with a Sauvignon Blanc of course, but keeping the reds with reds and the whites with whites. In the interest of not having several partial bottles around would you pour the rest of a Malbec in with a Zin or maybe combine a Pinot Noir with a Cabernet Sauvignon? Remember this is for cooking not drinking!