This is why #ZeroWaste as an aesthetic, all those reels of someone in a perfect kitchen waving a Kilner jar allegedly containing a year's worth of waste, is nonsense. For a start the seals on Kilner jars eventually perish & if you don't want to be picking bits of orange rubber out of your muesli you need to replace them. This replacement came in a packet of 12 in 2 plastic bags (which I threw away before thinking to take the photo and don't really fancy fishing back out of the bin).
@afewbugs I like using old (or new from the poundshop) silicone baking trays or mats to make new seals for that sort of thing. They won't degrade like the rubber ones. Compass cutters are a very useful tool.
I just installed two CCTV cameras using seals cut from a baking tray that was too disgusting to cook with but perfect for making a seal or four.