I don't have one single bag, rather everything I own I keep in some kind of bag/pack. I work with computers for a living as a consultant so I have everything on my laptop, tech info/manuals, etc. Have a big software collection, test servers/routers/etc. Then my different toolkits, bags/etc. I like to have everything setup, for anything. Say I have to go out of town to a client site, I can grab my laptop, hotel bag and go. House catches fire I grab whats most important. Nukes hit and laptop is fried, leave it and take a different bag.