This is the stool I use. Keep it in the back of the truck along the side up by the cab (black thing beside the gas cans).
https://www.walmart.com/ip/Folding-Step-Stool/38437780
Cheap enough to not flip out if some body steals it. Also works to wash the windshield.
I also like a toolbox that sits below the rails. Wife found it cheap on Facebook Marketplace.