Whenever possible look for tools that multi-task.
They may look goofy but toss a couple of those head mounted flashlights, preferably the LED type that have red output, too. You can use those and keep your hands free. The red light won't wreck your night vision.
Get a QUALITY multi-tool. I know the owner of Leatherman is a huge lib, but he makes good stuff. Buy one.
If you wear glasses, get a spare pare. Those could save your life.
Think about packing a small "Go Bag" in a Camelback type pack. You can fill that with water and go. You'd be surprised at how much water you'll got through if you have to boogie out of someplace.
I keep some beef jerky and trail mix in mine. A quick meal and some fresh water will keep you moving. Toss in some of those chem-lights. They go stale after a year or so so be sure you keep them fresh. But they're light and can be used for a lot of things.
Have you got a compass and a map of the local area? Toss one of each in there. Keep a spare pair of socks and some comfortable walking shoes in there.
Grab one or two of those cheap makeup mirrors and toss them in there. You can signal with those as well as look around corners.
One day soon I'll itemize and post the contents of mine for review and comment.
Hope it helps.
I use those too but hang around my neck - hanging around the neck I can see all around me instead of just straight ahead and no blinding someone when you turn to look at them!