These are very cheap in France but UK shops such as Cargo Lakeland and Homebase sell them reasonably and sometimes there are good deals on Amazon. Kilner are good but there are other makes - check they are dishwasher proof before you buy - with some of them the metal corrodes in the dishwasher. With them you can make stocks, soups and sauces in large quantities and have them ready in portions when you need them. Read up online or in a book about preserving to make sure you do it properly - it all depends on getting a vacuum seal so it can't go off. You can also buy fruit & veg when they are cheap in season or fresh from your garden and preserve them for times when they are less available.
I prefer the Kilner ones with replaceable discs rather than rubber rings - they come in quite small sizes so I can leave individual portions for my student son to feed himself bolognese at whatever time suits him.