For a light day trip
Here’s what goes into my emergency hiking back-pack – some water, light back-packing food (trail mix, chocolates, Belvita cookies, protein bars), sun-screen, bug-repellent, first-aid, analgesic, water-proof pouch for cellphone (a must have since I bricked my Pixel 2 in Everglades in this trip), hand sanitizer, small pack of soft tissues, small towel, portable selfie stick, extra face masks, battery juice pack with charging cable and some pennies to throw in the wishing well. Having spare change clothing (for rainy days and impromptu aqua frolics) and extra jackets (for wintry weather) in the car is strongly advised too.
For a long road trip
Download local Google maps for your destination. The cell reception could be patchy especially if you are going for camping/wilderness resorts.
Check the toll using TollGuru and make sure your car highway pass would work for the entire journey. We discovered the hard way that Illinois I-Pass does not work in Florida.
Enable GPS sharing between a few people in the trip. Calling people in different cars to know where they are is so old school and inefficient.
Keep extra cash. Once when we were coming back from Pictured Rock, one of our friend’s car got pulled over by a cop and we had to shell out ~200$ cash for the ticket, otherwise we would have needed to make a court appearance in a remote county precinct. Luckily, we had extra cash.