(+) What Format Should You Use to Store Your Files?

One question that pops up frequently is: "What format should I use to save my files?" The question is often asked about digital pictures. Should they be saved as JPG or PDF or GIF or PNG or TIFF or some other format? Similar questions are often asked about word processing files, although there seem to be fewer options available. I thought I would offer a few suggestions and also tell what works for me.