My friend brought game bags for elk this year that looked like queen bed sheets folded in half. Could have nearly put the whole animal in there. We just used the extra material to keep blood off our packs.
That said, I have also used literal pillow cases as game bags for deer. Last year, while I still had my first deer hanging in bags, I was planning to go back out and Walmart was out of the cheap game bags. I bought some whit pillow cases, washed them with baking soda to get any manufacturing chemicals out, and used them to pack my Buck out.