Mark, have you looked at this source for supplies and equipment:

Survival Resources
Look in the areas for water purification and shelter.

There are two items in particular they have that I have never seen anywhere else:
The Aqua Pouch Plus: has a filter, sturdy water container and purification tablets that all fit in your pocket or a small survival kit. At $12 it is a good addition to your kits.

The Orange Survival Bag: a very large, strong, and orange plastic bag. Serves as a shelter, signaling device or poncho. At $5.50 it is more expensive than the contractor bags from Lowes or Home Depot, but this one is larger, thicker, and orange.

Shelter and water are arguably the two most important components of a survival kit, and this is an excellent basis for any kit.