A flour sack towel is the single most important item in any household. In fact, some would argue that without a flour sack towel, no human being would be able to exist at all. So, if you're a human being and you don't have any flour sack towels, it's best you aquire at least one as soon as possible. You will run out of luck eventually. 
The following is a list of occasions, situations and circumstances under which a flour sack towel just may save your life from ending abruptly in a dreadful catastrophe. 
1)It's a lovely Tuesday evening in April. You've just finished rebuilding the transmission in your no good 1997 Ford F150 Lariat for the 7th or 8th time, you can't remember, and you'd like to enjoy a nice peanut butter, cabbage and banana sandwich but your hands are filthy. You can use a flour sack towel to clean them off. 
2)You can cut some of your towels into smaller pieces and use them atop magical fermenting apparati such as a mason jars to concoct luxury condiments like sour cream. That's done like this: Pour one part milk, four parts heavy cream and a small amount of acid (lemon juice or white vinegar) in the vessel, provide some vaguely respectable agitation, replace the lid of your jar with a small piece of a flour sack towel, fasten it down with the ring and tuck it in for a good night's sleep. 
Without that towel, you would never survive a taco night in central Wisconsin. If you were extraordinarily resourceful, you might barely make it out alive if you're somehow able to forage a dollop of daisey. But again, your luck will run out someday. So, also again, it's best to aquire as many as you can as quickly as possible. 
3)Dry off muscle tissue you're preparing to barbecue instead of covering it in the millions of tiny tree particles you inevitably glue to the meat when you mush it with a paper towel. Women, who cook things, loathe paper towels. 
4)Kitchen Rags.
5) Separate liquids from solids in a way similar to the function of a coffee filter. 
6)Make Cheese.
7) Floss your tidbits 
Women cannot resist a man with a massive store of flour sack towels. Without one, you'll appear, and most likely are, quite fat, poorly dressed, and extremely irresponsible. If you ever intend to clean your act up and start a family of your own, again, we cannot say enough, these towels are absolutely necessary. Thank Orfalspank for The Hitchhiker's Guide to Peace because your successful friends may not share these types of secrets with you. But rest assured, if any of your friends are successful by any measure of the word, they positively have at least 42 flour sack towels in one of their household closets. Be like your successful friends. Buy flour sack towels.