There are several items that I often suggest be included in your survival kits, yet don’t really fit neatly into any single category because they are so multi-purpose. Most of these things are very inexpensive and will certainly come in handy during a survival situation.
Surgical tubing is wonderful stuff. It is hollow and stretchy and has several uses. You can use it as a long straw to pull water from hard to reach places. This is also the same stuff that is often used for commercial slingshots and obviously would work well for a DIY one too.
Contractor grade trash bags fold up very small, fitting into almost any kit. Yet they have a wide range of uses. Stuff one with leaves and grass for a makeshift mattress. Cut holes for head and arms to make a rain poncho. Just lay it flat on wet ground to have a dry place to sit. Hold it open during a rainstorm to collect water.
Glue sticks, the kind that are for hot glue guns, are incredibly handy to have. You don’t need the gun, of course. Just hold the glue stick over a flame until it softens, them smear it where needed. Be careful as the soft glue will be hot, which should go without saying but….
Zip ties are, to my way of thinking, almost though not quite, as useful as duct tape. They are wonderful for attaching gear to your pack, lashing limbs together for a shelter, or any of another hundred uses. There are types of zip ties that can be undone, instead of needing to be cut off, but they are more expensive.
What sorts of odds and ends do you have in your kits?