A valve stem core tool. I got one decades ago and its saved lots of cash through the years. For instance you have a tire with a slow leak and the tire guy can't find it? It's not the tire, it's the little air valve in the stem that's leaking. Its barely an inch long and small enough to fit inside the stem on a tire. It's used to remove or install a valve core. I keep it in a container of specialty automotive tools inside my main tool bag.
Sort of funny, decades ago I shared a townhouse with a navy buddy. It had assigned parking. A lady visiting her BFF kept parking in my roommate's spot. She wouldn't stop when requested. He didn't slash her tires. Instead he borrowed my core tool. A couple of flat tires later and she stopped parking in his spot. He just removed the valve stem core, the tire wasn't damaged. She just had to go through the annoyance of changing the tire, taking it to a shop who replaced the valve core and aired it up.
I thought... in a bug out situation you might not want people following you... such a tool might come in handy. Especially if you wished to double back and "acquire" that vehicle later.