After the SHTF knowledge of how to make stuff (soap, pine tar, glue, concrete, gunpowder etc) that our ancestors use to make will be lost to most people. All these useful substances will greatly impact your survivability. Things such as modern glues will be lost and are easily replaced... IF you have the knowledge required to make your own. Here is a list of various non-edible and usually non-medical substances, usually liquids, that you can make for yourself IF you have the know how!
This list is not complete and is ever growing. If you were looking for a link to some material substance here but did not find it, then send me an email and I will try to bump it to the top of my list of things to include here.