I found everything I needed to make a decent first aid kit for under $10
DIY Car Kit. This would really come in handy (in the middle console or glove compartment) for the smaller things!
Great use for the 'days of the week' pill organizers - You could print labels and attach them - Perfect for travel
Road Trip Essentials With Free Printables
Our must-have snacks for road trips! Is a road trip the same without munchies? livelaughrowe.com
40 Free Road Trip printable activities
Summer Emergency Car Kit whats in yours - NAPA Know How Blog
Keep a tissue box full of plastic bags handy for wet swimsuits or muddy shoes.
Repurpose a dollar-store cereal container as a sealable trash can.
Stick a couple of silicone muffin cups in your cup holders to catch all the dirt that ends up in the crevices.