for water I would suggest using Micropur tabs (or equivalent) they are very light and take up little to no room (1 tablet/liter of water)- I keep 12 tabs for my 3 day kit
I also throw in a Aquamira straw filter- it weighs less than an ounce and costs less than $10
http://www.aquamira.com/military/aquamira-frontier-filter
for carrying water - a couple of 1 liter platypus water "bottles"- these are tough little bottles that weigh less than an oz and can be rolled flat
as someone mentioned above a bandana makes a great pre-filter for "thicker" water
I would suggest an emergency blanket/bivy added to your kit, in addition a poncho tarp weighs very little and rolls up nicely taking very little volume- a half dozen ti stakes and some guy line and you have a nice little shelter (you also have a nice poncho to boot)
for tinder "tinder tabs" work great and weigh almost nothing (as does the sparklite that is often sold w/ them)- I add some firestraws to my match safe- easily made by taking a section of straw and sealing one end (carefully w/ a lighter and pliers)- stuffing PJCB strands into the straw- leave a little room and then seal the remaining end.
my matchsafe is a K&M complete w/ nice little Suunto compass, the matches are REI stormproof ones- I have not found a match that equals the performance of the REI ones (and I've looked).
I also agree w/ the above poster that a small cook kit would be something to consider adding as well- you can put together a small kit that all nests into a 600 ml pot/cup that weighs less than 8 oz -including the stove, windscreen, fuel, spoon, fuel, a mini bic lighter and the pot itself.
with some careful gear selection you can put together a pretty tidy kit that fits into a small daypack/fannypack
I also throw in a Aquamira straw filter- it weighs less than an ounce and costs less than $10
http://www.aquamira.com/military/aquamira-frontier-filter
for carrying water - a couple of 1 liter platypus water "bottles"- these are tough little bottles that weigh less than an oz and can be rolled flat
as someone mentioned above a bandana makes a great pre-filter for "thicker" water
I would suggest an emergency blanket/bivy added to your kit, in addition a poncho tarp weighs very little and rolls up nicely taking very little volume- a half dozen ti stakes and some guy line and you have a nice little shelter (you also have a nice poncho to boot)
for tinder "tinder tabs" work great and weigh almost nothing (as does the sparklite that is often sold w/ them)- I add some firestraws to my match safe- easily made by taking a section of straw and sealing one end (carefully w/ a lighter and pliers)- stuffing PJCB strands into the straw- leave a little room and then seal the remaining end.
my matchsafe is a K&M complete w/ nice little Suunto compass, the matches are REI stormproof ones- I have not found a match that equals the performance of the REI ones (and I've looked).

I also agree w/ the above poster that a small cook kit would be something to consider adding as well- you can put together a small kit that all nests into a 600 ml pot/cup that weighs less than 8 oz -including the stove, windscreen, fuel, spoon, fuel, a mini bic lighter and the pot itself.
with some careful gear selection you can put together a pretty tidy kit that fits into a small daypack/fannypack
