Definitely tools. I keep so many tools in the back of my truck it's not even funny. Literally enough tools to almost anything the truck would need in a parking lot. Hell, I changed a couple injectors and all my o-rings in my school parking lot a while back.

Truthfully, you don't even need the brake switch. You can pop the shifter shroud up and actuate the shifter lock by hand until you can get a new one.

I do carry an old serpentine belt for an extra, a quart of oil, quart of brake fluid, gallon of 50/50 antifreeze, tube of RTV.

 

That's why you only get 12 mpg.

If you take out the HF 3/4" drive set you might get another mpg.

......

 

I've been told that, but nothing really effects my mileage. I've tried a tank with no tools, no change. Tried a tank with tools plus my hi-lift on the roof, no change. Tried pulling 7k lbs, have all my tools, and the hi lift on top, I lost 1 mpg. It's insane, but it stays the same pretty much no matter what.