Jock Itch: Buy a box of Borax (the old "20 Mule Team").
Fill an old pill container with the borax and store the rest of the box. A whole box of Borax will be enough to last many years.
After your shower, while the skin is still damp, dip a finger in the jar of Borax and dab it on the affected areas. If fungus is in the groin area, one finger dip per side. You need very very little of this stuff, a small pill bottle full lasts me months.
Fungus thrives in dark, damp high pH environments. The Borax is boric acid and applying this to the skin lowers the pH of the skin making it slightly acidic (the way skin should be) and inhospitable to the fungus.
Do this once a day after your shower and continue as an everyday routine. The athletes foot or jock itch will be gone in about two days. However, if you skip a couple of days it will come roaring back.