The second thing I never leave home without is my knife. I mean, come on, when are knives NOT useful? You can open boxes, pry things apart, stab people, etc. The uses are endless! I carry a Smith & Wesson M&P. It is a spring assisted knife so it is easy to open with one hand. It is a carry over from when I was a firefighter. It is an amazingly durable and reliable knife.
And last but certainly not least, the ONE item that EVERYONE should always have with them... A good Multi-Tool. These things come in a variety of options, sizes, qualities, and finishes. A good Multi-Tool can save your ass in a number of ways. I don't carry a tool kit with me all the time so when I come across some small repair I can usually just pull out the Multi-Tool and get it taken care of without having to carry a ton of different tools around. My current Multi-Tool is the SOG Power Assist. It is fairly simple as far as Multi-Tools go but it does what I need it to do; day in and day out.
So those are the three things that I absolutely cannot live without. I feel completely naked if I don't have these three things on me at all times. Now, some of you might say that carrying a knife AND a Multi-Tool is overkill. After all, most Multi-Tools have a knife in them. So is this overkill? Absolutely. I'm a MAN, dammit. Overkill is what we do. Especially geeks. And while it very well may be overkill, there really is no substitute for a high quality knife. While some Multi-Tools, such as the SOG shown above, contain pretty decent knives, they will never compare to a high-quality stand-alone knife.
Now that you know what gadgets/tools I can't live without. What is your top three?