These are outrageously expensive when compared to the 2 litre bottles of juice, but obviously they only use happy apples to make the contents.
They run about 2-3oz capacity, usually with a pop-top, and are either in the juice or baby food section
The other great lightweight jars with a leakproof lid are urine sample jars. These are about a 2oz capacity, pretty tough, and leakproof with a flanged lid. It's always fun explaining to your hiking partners that you washed them out VERY carefully before you used them for bushwalking. Of course you can always use the ones with the brown lids if you need to differentiate jars.