Don't worry, you probably won't need any if this is your first time!
Just messing with you, you'll need at least 4. Some guys like the heavy duty canvas ones, but the light cheesecloth bags work fine, yet are more likely to tear.
It all depends on how far from a road that you get that record breaker. The last 3 elk that I have taken we brought out in 6 pieces plus the head. Now if you bone the meat out it will take a lot less but figure on at least 4. As far as bags I like the heaver cotton canvas type, then you don't have to worry about sitting the meat down on the ground while you rest and get ready for the next few yards. As far as where, most sporting goods dealers out here will sell the quality ones. But don't think that WalMart is a sporting goods dealer. Also when you find some I would recommend the ones for elk quarter bags.
I just did a quick search on Google for "Game Bags" and came up with this link. It is no recommendation but they look like fairly good ones.
After using pillowcases and cheep bags ,I got some excellent ,tho pricy ones from RMEF.I use lite ones for pack outs and then hang them in the heavy ones for security .They are washable and will last forever,they breath better too.
It depends on what i need them for as to what i use. Don't bother with the 1.99 ones you see at WallMArt. They are garbage. If you want something to put in your backpack for quarters, i think the Alaskan game socks work wonderful. They don't look that big but roll on and stretch and are tough enough you can tie a knot in the top and hang them from a tree with out the bag ripping. I usually include a Deer one or two along with the quarter bags in case you have an elk with large hind quarters. If its for back at camp, i have some of the heavier ones like you will find at sportsmans wharehouse. If i am going to get something out whole, a couple of sheets sown together work well. Also i picked up some fabric at the fabric store that came in a big tube(maybe yards of cloth always come like that ) sewed the bottom shut, and now i have a bag that will cover a whole elk.
Most important things to look for are:
1.Weave has to be tight enough that bugs can't get in. The cheapy 1.99 ones willl let small flys in.
2.Cloth has to "breathe" The air circulation is what cools the meat down and keeps it from spoiling.
3.has to be tough enoough that it won't easily tear when poked by a bone or snagged by a piece of brush.
As I sit and glass, which is common for hunters out west, I have sort of quickly discovered something I never learned when I was younger.
In my youth I had enthusiasm and spirit. In my middle to advancing years I have creaky knees, arthritis, and I tire more easily than I used to. Where I used to sit on the cold hard ground I now look for that soft spot to sooth my tired muscles. That leads me to my tip.
Carry your soft spot with you!
In my pack I carry an air filled, ultralight, camping pad....