Funky feet is the culprit of sweaty sandal feet and stinky shoes. Bacteria loves to hide out in the dark, damp areas under your soles. So be vigilant about cleaning your toes after a long day walking outdoors. If sweat is your primary issue, try a moisture-absorbing product like baby powder. The true problem could also be your shoes. Throw your soles in the washing machine (or the entire shoe if it's feasible). You can also pour a bit of baking soda on your flats to minimize odor.
Try: Ban Total Refresh Cooling Body Cloths ($3) and Odor-Eaters Foot & Sneaker Spray Powder ($7)