>>2313397Small cofin bivy, MSR pro - Packs to the size of a water bottle. Smaller options dont provide enough weather resistance.
Cheap Inflatable mat (eg Sleepingo) - Packs to the size of a water bottle.
^------------------and/or depending on cold-------------v
3mm foam pad cut to minimal dimensions for sleeping - Easy to fold and pack away to the size of a towel in your pack.
Sleeping bag liner or small down quilt (naturehike cw280) - Again packing depends on how cold it is. But shouldnt take up more than 15 by 20 cm at the largest.
Flat folding mini wood stove with alcohol stove (lixada make a few cheap options) - No bigger than having a thick coaster and a crushed coke can in your pack. Small bottle of fuel for when you cant use wood.
Water filtration is tricky. Technically can boil everything and use cloth for sediment. Compact filters dont work on heavy metals and/or viruses. Still, doesnt hurt to chuck in a sawyer mini.
Multitool for knife work and other odd jobs - Tiny, you dont really need a fixed blade.
Wiresaw for larger woodwork - Packs away to almost nothing, can attach to a stick for framing.
1 small back bladder - Compact available water that you can keep filled from the start.
2 Platypus silicone bottles - Pack to nothing and conform to shape. Best option for carrying additional water.
Baby bear cook pot - Packs flat to the size of large wallet. Use this for boiling and cooking needs.
Emergency food rations - Dense small 400 calorie bars in each pack. 2-3 packs is 7200-10800 calories total which should keep you in decent shape for 5 days. Takes up the most room at the size of a lunchbox with no ability to compress, but with the other listed items you should have enough room.
That covers most the bulkier items. Clothing is largely up to you. A raincoat can fit in your pocket. Neoprene/fleece-like pants and jackets can keep you warm with minimal base layers.
Reliability is its own rabbit-hole so some packable items involve sacrifices
