I just can't get enough of these Fido jars by Bormioli. They are high quality Italian glass jars with rubber sealing rings that hermetically seal stuff inside them. That means the seal is air-tight and the glass jar is essentially air-tight, so the useful life of the food inside is extended. The jars come in sizes from about 1 cup (1/4 liter) to 3 liters, which is about 3/4 of a gallon. The rubber rings can be washed and reused. When they lose their elasticity, they can be replaced with new rubber rings. I wash mine in the dishwasher and they come out just fine.
I don't recommend substituting another brand of jar for these. Ones with a plastic top are not impermeable to air. I tried them and they cracked with use or cleaning in the dishwasher. The steel ones can absorb moisture from the product and often come with silicone rings which don't make the same type of seal. Others have thinner glass or no ability to create the air-tight seal.
Why would any one want these for preparedness, and how are the jars frugal? Let me offer answers. The jars can be frugal in two ways. First, if you find them at Ross or Marshall's, they are often under $5 each which is a great price for what they can do for you. Second, they can extend the useful life of any dry food product that can spoil, go rancid or get stale after opening the package.
Here's how I use them: once I open a package of something, like a 5-lb bag of flour or a #10 can of something, I place the unused remainder of the product in one of these jars, seal the lid with a little wrist action and store. The lack of oxygen will limit the speed of food oxidizing or absorbing moisture from humidity. It keeps my flour from going stale when I put the sealed jar in the frige or freezer. Overall, these extend the life of foods by delaying the processes that cause the flavor to change.
The jars are also handy for storing tea bags, the second half of that bag of rice or beans from Bob's Red mill or brown sugar. If you need to use a large can of something from food storage, you can store the unused portion in a Fido jar and it will last longer. These are also clear, which has saved me many times from opening a new bag of something because I could SEE that I already had half-a-bag in a glass jar.
I don't use these for wet items, just because I have no experience with it. If you have, I'd love to see a comment about how to use them that way. Also, if you have used them for real canning, please share!