Using any .stl file and Tinkercad, you can easily personalize a 3D design of another designer from websites like Thingiverse or Yeggi.
Step 1: Finding a Design
Okay so I am not the most creative person. I would have to admit that the majority of my creativity comes in iterating another more creative person's design. So I knew that I wanted to create a keychain that represents our school. Our school district mascot is the Wildcats so I thought that I would start by searching for already created designs of keychains around the idea of cats.
I started at Thingiverse but eventually stumbled upon Yeggi.
Step 2: Thingiverse Design 1
I really liked the design on Thingiverse from Alajaz so I downloaded the .stl file. But I also wanted more. I wanted our school initials on the design which is where my favorite 3D software Tinkercad came into play. Tinkercad allows me to take any .stl file and import it, ungroup it, and make it my own iteration. So I was able to easily stamp the SP logo into the cat keychain. Unfortunately it wasn't a hit for all of my critics so I created a second design.
Step 3: Yeggi Design 2
So at this point I have to admit that I was ready to accept that my first design though not liked by all would have to do. I did one more search for 3D paw keychains and that is when I stumbled on Yeggi. Numerous designs were displayed that I could work off of and one caught my eye.
It was a Christmas design that I could iterate in Tinkercad to make it work for our school.