I've always used citric acid for canning, drying, making cheese, freezing, discoloration, Vitamin C preservation, and to inhibit content spoilage. Maybe I'll sprinkle citric acid on my fresh strawberries, which have such a short shelf life... I also use citric acid to my stash to reduce bitterness, enhance flavor. Generally speaking, all is needed is 1 tsp. per quart of water or juice. Preserves color of most fruits and vegetables.
I like Pat's idea on how to enhance the flavor of cola and root beer when mixing syrup to make soda.
All that said, my main purpose in purchasing 1 Kilo ($14.96) of citric acid is to keep my MegaHome 1 Gallon Water Cleaner clean of debris from the filtration process. Interesting enough, MegaHome does not mention citric acid as a way to keep my MegaHome clean. They should!
But, today, I also used it to clean the interior of a teapot whose bottom was significantly discolored. I was seriously thinking of throwing the teapot in the garbage! I filled the teapot with ordinary unfiltered water, dropped in 1 tsp. of citric acid. Instantly it went to work cleansing the crud off the entire interior, especially the bottom. It showed I have a beautify shiny copper bottom in this tea pot and now I won't throw it away! I'll simply use it.
I then used it to clean my knives, forks and spoons in the same teapot which was now clean and beautiful on the inside. I also did a dip in my MegaHome Water Cleaner as it was cleaning the inside with only 1 Tablespoon citric acid added to the water. Instantly it just cleansed a whole bunch of kitchen utensils, ever so easily. It only took a "dip" for the eating utensils to be cleansed, shiny and all the crud I didn't know was there, gone.
Citric acid is also must beneficial to fight wrinkles, maintain skin, bones, blood vessels, and skin and a most usable additive to anyone's stash. A paste of citric acid treats some skin problems (mild acne) clogged pores, sun tanning, and dark spots.
I also use a Blue, Green or Red Sharpie, to write everything I want to know about a product on the outside of the plastic bag, including how much to use daily. I then cover the writing with clear plastic tape, so the writing is preserved.
The sometimes a challenge bag? I cleanse the track, use my fingers to engage both sides of the track, and seal. I then fold the top over, to engage a double-seal, and then attach 3 clippies, to ensure the bag remains really sealed. Bulk Supplements folks have told me if they change the bags to other ways to hold their contents, the products would have to cost more. I love the fact I can put everything I want to know about a product on the exterior of the bag, and truly remember the important issues about the product.