Yep - once you get beyond basic first aid gear, one of the next most advanced things I would get is a stretcher.
People don't have to be very injured before they are nonabulatory.
If you need to move an injured person or get an injured person in/out of vehicles, then a stretcher is pretty much essential.
If you are transporting a patient in a vehicle, then a stretcher makes it much safer (easier to immobilize them in a flat space of a suitable vehicle on a purpose built stretcher).
You can get mil surp stretchers - the best one is made by North American Rescue Products and is called a WALK (Warrior Aid Litter Kit).
They consist of a folding stretcher in a backpack - with lots of space for other first aid gear.
North American Rescue pays attention. We listen. We learn. We act. We develop products like the Warrior Aid and Litter Kit™ (WALK®), our innovative and reliable response to requests from Warfighters and Tactical Healthcare Professionals to re-think the purpose of vehicle life-saving kits and...
www.narescue.com
NARP sells them for about $1700 - but you can find Mil Surp ones with expired aid supplies (but a perfectly fine litter) for a fraction of that cost.