Stuff to carry on you:

cellphone
folding knife
writing pen
whistle
firearm w/spare mag
wallet w/contacts-meds-allergies infocard
emergency money (separate from wallet)
Tylenol/Advil
1xAAA LED flashlight

In the car/truck:

jacket/rainwear
water
snacks
car stuff (maps, bungees, duct tape, paracord, tow strap, tiedown straps, etc.)
larger LED flashlight
umbrella
folding chair