I use Remington game bags that I have picked up at Walmart, $7.00. I have washed an reused them which is nice, but paying $7 every now and again is to painful. Only other game bags I have used were the Alaska Outfitter ones you can get at Cabela's. I didn't care for these, they got torn up pretty easily.
They way I have figured it, you need 4 bags for each quarter, 1 for backstraps and tenderloins, 1 maybe 2 for miscellaneous meat. Of course, if you plan on boning the animal out, you could probably get away with putting both front shoulders in one bag. Some folks use 1 bag for the cape as well, but I haven't done this.