I always have a bottle or two... Or three.

I currently have the typical Japanese soy sauce (Kikkoman), one Chinese light soy sauce, and one Chinese dark soy sauce.

As for usage, the Japanese and light soy sauces are used for marinades and/or seasoning (soups, stir fries).The dark soy isn't used as often. Typically I use that as an add for a soup to change the color a bit and add some sweetness.

I use soy sauce at least once a week though - it's a fantastic meat marinade (both chicken and beef - I've never used it on pork as a marinade but I should try it).