There's a few things I'd attempt to do (I don't know the exact size specifications) but I hesitate to mention them because I'm a fan of gutting kits and adding a lot of new things which might be inconvinent if budget is a concern.

I assume this is carried in addition to your normal hiking gear...

Personally, I'd try to....
-See if doug's kit will fit inside, and if it will, replace the match/compass/whistle with it.

-There are first aid kits that come in packages similar to doug's kit. If you can pick one of those up, it should save you some room. Naturally you can gut that and design it around your needs too.

-Replace the flashlight with a photon II or III, or other LED of your choice. They're tiny, they last a long time, and they're useful for signalling... not so much for finding your way, but that's what a surefire is for <img src="/images/graemlins/wink.gif" alt="" />

-Agreed about the cup. It's a good idea to have 2 things that can hold water, that way you don't dirty up your primary drinking container with mucky water that hasn't been filtered or purified yet. You can also boil in it.

-Go ahead and get some purification tablets. I wonder if those survival straws are any good (as a backup?)

-You might consider adding a few items like 550 cord and small eye screws. Always useful. Eye screws can be screwed into trees and fishing line or 550 cord tied to each, that way you can drape a poncho over it for shelter. You can screw them into trees on opposite sites of a body of water, and lay fishing line/550 cord across to lay a trout line or gill net of some sort.

-Consider replacing the swiss army knife with a leatherman micra. Gives you all the features (except the toothpick) and makes for better sissors.

-Again, not sure if room is there, but a full sized multi-tool might be useful as well. Some have fish scalers on them, some have saws, etc

-Keep the poncho and space blanket

-Make sure you have nice sized ziplock to carry stuff when your water container is full of water!

-Toilet paper! MRE toilet paper works, small bag of tissue, anything that'll fit. You can use it to help light a fire, and it sure beats pine cones when it comes to comfort <img src="/images/graemlins/wink.gif" alt="" />