I'll +1 on Mike_H's recommendation of a Doug Ritter's PSK as just about the best (IMHO) featherweight survival kit. If you have the extra cash, about 30 to 35 bucks and the time to get one before you go on your hike I'd say get one of those and stash it in your pocket. Its about 4oz. And the size of a slice of bread. Bonus point for if, God forbid, there is a accident and you are seperated from your pack, it will still be with you.
If you are adverse to this I'd say at a minimum to add to what you do have is a compass, some water treatment tabs (just in case) and a "space blanket" for emergency shelter. American Medical makes a great one, I'd suggest with going for the two person one. Not much bigger profile in pocket/pack, can bail out someone else by sharing, can wrap yourself up without stressing the material by making it too taught etc....
Good luck and have fun!
Welcome to the forums new guy!

-Bill Liptak