Prolonging the life of chemicals
Here are a couple of suggestions for you.
Firstly if you are able to aliquote your chemicals properly which means you have to know how much of each ingredient goes into a given volume you will be able to mix what you need. Of course you need to know how much of solutions A,B C etc to use and to measure small volumes with accuracy. Hypodermic syringes and pipettes work nicely.
Secondly, If you have access to a freezer you can mix the full kit and put it into individual glass bottles. Do not fill the bottles or you may have them break as they freeze.
Thirdly, If you do not want to or unable to freeze your Chemicals you can fill the GLASS bottles to the top. As you use chemistry from a given bottle you can add marbles to it at the session's end to eliminate air space. A photographic supply firm Techcheminc...www.techcheminc.com sells marles for $3.00 for approximately 100. This BTW is a very nice firm with which to deal.