Israeli battle dressing. They can serve as a tourniquet, but are designed to be as close as possible without actually cutting off all of the circulation. They cost a few bucks and take about 5 minutes to figure out how to use... so buy a spare that you can open up and play with. You don't want those five minutes to be in the field while you are bleeding.
I have one in every bag, pack, glove compartment, desk drawer at work,....
Other things for the field...
Triangle bandages are very versatile for the space/weight. Can make a sling, can be used to tie a brace to leg or secure gauze.
At least one way to start fire, two is better.
I carry the israeli battle dressing, Celox (quick clot), 2 lighters, fire stick and betadine. That's about 6" x 3" pile. My much more expansive kit is always in the truck.
Some items I have for folks to consider for their vehicle...
Small suture kits, multiple sizes of butterfly bandages, betadine or saline washes, antibiotic, amonia tabs, Bayer for pain or heart attack, medical tape, gauze, Ace wraps, ankle brace, tweezers, small light, reading glasses, rubber gloves, wool sock, wool hat, body warmers to create hit, emergency blanket to help trap it... That's a quick list from memory. There are great lists online if you want to build a nice kit.
Please read the warnings on Hemostatic agents, iodine, betadine, etc. so you know the choice you are making before using it.