The first thing to do is to avoid the problem. Don't purchase more than your going to use. Find out what alternatives there may be for accomplishing the same results. An example may be to hire someone who knows what they're doing to get rid of pests rather than buying several different pest control products that may or may not be effective. It may be less costly in the long run.
Many people buy the product and never get around to using it.
Don't take it home until you're ready to use it, and only buy the amount you need. If you find yourself with extra, find out if friends, neighbors, relatives, or co-workers can use it. There are less harsh products that may work as well as the stronger ones for what you need to do. Some of these may be more easily disposed of. Never dump these products into any sewers or drains unless the instructions indicate that you can.