Thanks to Marilyn for sharing this idea with us!
Cut out a boot print shape on box cardboard. Take white glue and make squiggly lines (i.e. treads for the bottom of the boot). Have kids steal some sand from the sandbox and sprinkle on the card - shake off excess. While it's drying, make a child's footprint with paint on some white paper. Print a message, something like "Dad, I'm growing to fill your footsteps, I love you, from Junior", or something that is more appropriate for your family.
When all dry, glue the white paper to the back of the boot print and
ta-daa! This is nice for those families that have dad's that only wear ties to weddings and funerals. :)