Looks to me like the bottom line is that you don't have enough room for a do-all PSK. Anything you add will help, but you need to cover the essentials. I would want the following items for a true wilderness PSK:
knife
compass
whistle
signal mirror
sunglasses
first aid kit with antibiotic ointment, ibuprofen, immodium a-d, benedryl
space blanket or bivy
garbage bag
water container (1-2 liter bladder)
chlorine dioxide tablets (iodine is not as effective) use your bandana to filter out the silt.
bandana
multiple fire starters: lighter/matches/firesteel
tinder: TinderQuik tabs, PJ cotton balls, Esbit tabs
16-22oz pot for cooking/boiling water
wire saw
fish line
nylon seine twine and/or paracord
small gauge wire for snares, repairs
duct tape
small fishing kit
scalpel blades
single-edge razor blade
flashlight/headlamp and spare batteries
sunscreen
bug repellent
This will all easily fit in a drawstring style pack/back and leave plenty of room for your extra clothing and food that you should be carrying in the woods at all times. That can be as simple as a fleece top and a couple granola bars. I add ten or so peices of hard candy to my kits for quick energy/morale. The PSK listed would actually all fit in a small stuff sack.
My sheath mounted PSK has the absolute minimal essentials and assumes that I have my other survival and hiking gear in my pack. It is always carried with me to cover if all my other gear is lost and I'm in the ultimate SHTF situation:
Entrek Javalina in a Kydex sheath
Generic multi-tool sheath strapped to the sheath
Silva keychain compass
SAK Classic Stayglow
ACR whistle
Swedish Firesteel
Spy capsule with TinderQuik tabs
Lansky Dogbone sharpener
LED micro light
Wedged between the two sheaths is a paracord braid made with 8' of line.
Another way to carry a kit is to use a Nalgene bottle with the goodies inside and nest it in a pot made to fit the Nalgene. That in turn can go in a holster made for the Nalgene, a stuff sack, or in a shoulder strap rig made for Nalgene bottles-- Nalgene and many others make them.
A variation on the Nalgene idea is to use a
waist pack that has holsters for two water bottles and a small pocket between. You can carry water in one or bothe bottles, or one bottle with water and the other holster with a bottle or stuff sack full of gear and more gear in the pocket. You could carry a fixed blade knife or machete, etc on the waist belt too.
There are a number of smalllight packs that are really just a stuff sack with straps.
REI offers the "Flash" model that is perfect for carrying a PSK and leaves room for a fleece top, food etc.
My favorite day-hiking rig is to use a hydration pack with enough extra storage to keep all the essentials in it.
I've fiddled with many kinds of belt rigs like ammo magazine pouches, and they all run into the same compromises that you have run into with the canteen rig. Anything is better than nothing at all, but a little more room and another pound of gear can really make a difference in being able to deal with weather, bugs, navigation, signalling, first aid, and fire-making. Some redundancy and "layering" of gear on your person and in you pack can help cover the various scenarios you might find yourself in.
If you want to keep the canteen arrangment, consider adding something like a
SAW ammo pouch or another
closed-top canteen pouch to hold the rest of your gear. If you want a shoulder strap with multiple uses, consider making a paracord braid like the one used for
bracelets. The ratio is roughly 1:12, so a braid long enough for a shoulder strap could have 50+ feet of line in it. You could make a belt or shoulder strap with nylon webbing and plastic buckles like the ones used on backpacks. If they aren't available in your area, buy a beat up pack at a thrift store or garage sale and cut the hardware off it-- I've bought several packs for less than the hardware would cost new.