The discussion about tourniquets got me thinking about high bang for buck medical devices in disasters that disrupt our first world health care delivery system and degrade it to a third world level. A tourniquet stops the arterial bleed, but at the cost of slowly killing all the cells distal to it. Definitive care requires tying off or repairing the artery. closing the wound, maybe amputating the limb. Civil war era medicine, maybe. We could get there with an EMP, a really big storm,big or failed state level social collapse, anything that disrupts power grids and transportation, isolating portions of the population.
Parenteral fluid replacement equipment is a nominee. The body can heal itself quite remarkably if hydration is supported.
proctoclysis is available without the issues of needles and injection skills.
Hypodermoclysis , involves injection skills but does not require venous access.

Both of these methods are in current use in pediatric and geriatric medicine, and are simpler and safer to manage than IV therapy. That said, IV threapy was restricted to physicians until the mid 1950's, and has subsequently been added to nursing and paramedic practice with great success.