I am building a stone walkway. What can I plant in the cracks
that will take the sun and that I can walk on?
Creeping thyme would be ideal for your needs. It will do well in sun, and
can withstand foot traffic. Colorado State University Extension has useful information on groundcover plants for dry conditions.
Leptinella, or brass buttons, is another option.
Chamaemelum nobile likes sun and will withstand light foot traffic.
The website for Stepables, a company specializing in groundcover plants,
allows a search by plant characteristics.