Welcome to APUG and film developing.
If you haven't already done so, you should download the data sheet for the developer, and read the Ilford website information for the stop bath and fixer. The Ilford website also has a Getting Started section that you should read and maybe print out sections of: Dead Link Removed
Once mixed to working strength, some chemicals are designed to be re-used until they have been used up.
Once mixed to working strength, some chemicals can be re-used under some circumstances.
And once mixed to working strength, some chemicals should be used just once ("one-shot").
The Photo-flo is best if you just put two drops in a litre or so, use it that day for as many rolls as you are developing that day, and then discard it. The concentrate should last a very long time.
The Ilford data will tell you what the capacity of the fixer is in rolls per gallon/litre. You should mix up one litre/34 oz and keep and re-use the working strength fixer in a bottle. Use the capacity information in the data as a guide, but do regular clip testys, as described here, to ensure the fixer is still good: (there was a url link here which no longer exists)
Stp bath should basically be used "one-shot". If you are going to do a bunch of development over a couple of days, you can re-use it over a day or two, but longer than that isn't a good idea.
If you are just developing a couple of rolls in a day, it should be fine to mix it 1+39 instead, and discard after use.
D76 is more complex. Many people use it diluted instead of at stock dilution. That permits development of more rolls, but you must use it one-shot if you do. You also need to be sure that you use at least 250 ml of stock (before dilution) per roll in your tank.
If you re-use the D76, you need to follow the instructions for increasing times.
Empty soda bottles with screw on lids and clear labels make good storage containers. Datatainers or other containers designed for photography are also good. Do not use the accordion bottles.