Checklists might not seem very 'Kerbal' but trust me, the next time Jeb runs out of power on the far side of the Mun you'll wish you'd used one.
The KSP build checklist notepad is a handy tool that you can use during the construction of your rockets. Kerbals have terrible memories, so by ticking off each component as you add it to the ship you'll avoid any embarrassing realizations mid-mission.
Each notepad consists of 100 4x5.5 inch pages gummed at the top and backed with a single piece of cardstock. Checklists are printed in black ink on white paper.
Want to print your own? Be my guest! Head over here to get a pdf or vector source file: http://theflyingdeveloper.com/ksp-checklist/