Stop bath is best used once and then discarded, unless you are doing a bunch of rolls on the same day (or so) in which case you can re-use it as long as the colour doesn't change.
For fixer, I mix up 1.25 litres at a time and re-use it until the manufacturer's capacity is 3/4 reached, or clip tests indicate the clearing time has increased to twice what it was when originally mixed.
My 1.25 litre bottles originally contained Trader Joes' sparkling water. Now they have no original labels, and are identified with masking tape and warnings.
I mark the usage (number of rolls) on the masking tape.