Condoms can be used to carry water from the source to the camp. They hold about a quart, just have to be careful... They degrade in the heat, become fragile. Not the best way, especially for repeated use. I would recomend an Israeli pilot water bag or a camelback type insert for the pack itself for more durability. And a stainless water bottle, single wall, for boiling water and carrying water over long distances. Make it your regular waterbottle... Water is most important, and clean water is key.
Add iodine water tablets, bic lighters, swiss army knife with a saw for building shelter, LED flashlight or headlamp. I love the AAA battery LED Tikka zipka headlamp and the Fenix LED AAA mini flashlights. Few extra AAA batteries will last a long time with regular use. Food can be a lifeboat ration, durable 'brick' of hardtack, 3 days worth of meals @1200cal a day. Supplimented with jerky, trail mix, you will have a good headstart.
Space blanket or bivy bag. You can get a 2 man space blanket that makes great shelter, especially with a reflector fire. Extra jacket depending on season. Wool cap and socks. Sturdy shoes or hiking boots... Dressing for the wilderness, wool, poly fleece, gore tex, and hiking boots will solve alot of that storage space issue.
Good premade FAK is Adventure Medical Kits, add extra bandages, betadine pads, CAT tournequet, packet of Celox. Israeli bandage, celox and CAT you can handle any SERIOUS extremity wound rapidly and effectively.
With the Tylenol #3 bring a small copy of prescription, or use the prescription bottle- add regular tylenol, advil, naproxin to fill the empty space, pack with cotton balls. With a little triple antibiotic ointment, a good tinder to get a fire going fast. Otherwise you are carrying around contraband and could face charges...