I brought a couple tubs of powered buttermilk from the US when we moved. I like that the best, I just add the power to the other flour stuff and add water to the liquids.

But, I've used the milk+vinegar for some of the recipes I have (some specifically call for you to sour the milk, not use buttermilk).

I took a look at my joy of cooking from 1975 (huh, didn't realize it was that old!). There they say to substitute it with yogurt (1c buttermilk = 1c yogurt). For 1c cake flour, it says you can use 7/8c sifted all purpose flour or 1c less 2T. But I think someone mentioned that Coop has cake flour. So far, I've just avoided recipes that called for cake flour, I still haven't made it to Coop by us to see if they have the cake flour.

From the Baking Ingredients thread (post #18 - don't know how to link to that one in the thread)
For recipes calling for cake flour, sift together (for 1 cup):
1 cup, minus 2 Tbsps, all-purpose flour
2 Tbsps. cornstarch (corn*flour)

Also, someone went through and compared all the kinds of flour on their blog. I used this info when we first got here so I could kind of figure out the types.