Empty soda can
Some playdoh (or any suitable replacement)
Step 1: Cutting up the can
As you can see in the picture, I had already started cutting the top of the can.
Now you have an empty can and its top. Dispose of the can top.
Step 2: Bending the rim
If there are any deformities still present, use your judgement to press and squeeze (the can) to make it as round as possible.
Step 3: Put some weight under the can
Step 4: Enhancements
I have attached the calendar pdf. Print it at 100% scale so that it fits perfectly. Cut the page at the top left corner of January and keep cutting half an inch or so beyond December so that it fits properly.