Good thinking
You could have also used a closed cell sleeping pad, The backpacking merit badge book/ scout book (LOL) , hiking poles , water bottles all these would work
If you are to add an item to your first aid kit I would suggest a Sam splint (many uses) and light weight
To answers the question about AHA course. The answer in all basic courses is to call 911 so splinting is not an issue in most calls, plus the instructor had the option of presenting the splinting module
If you want practice at take that the very least WFA or WFR course