I have many papers that are 8.5"x11" and not many 12"x12" papers.

I choose a 12x12 paper and a 8.5x11 paper that cooridinate and use my fancy scissors and cut a few inches of the 8.5x11 paper off from the edge and go the length of the paper. Then take the pieces and glue them to the 12x12 paper a few inches apart.

This uses up more space on the paper and I don't have to keep buying 12x12 paper all the time.