Potatoes is a great choice for practicing. Not expensive if you screw it up (you won't lol). They can be peeled & diced the evening before and kept under water in a bucket overnight if necessary. No need to refrigerate for that. Use fresh water in the jars of course. NEVER add vinegar in the canner water, as some videos recommend -- it makes the jar bands rust. Nasty!

I have a Presto 23 qt, which allows for double decker pints. About eight years ago, it cost around $100. I hear a faint hiss this year, so I'll need to buy a new rubber gasket for its lid, as the original has dried and shrank over time. It still works, but I have to keep the heat up higher than if the gasket were in perfect shape.