I have an external framed Berghaus Freeflow light 32 Litre backpack, it is very light and weighs in around 800 grams.

For 2 Days I would add the following

Platypus 2 Litre water carrier and drinking tube and Pure Inline water filter. @ 200gms
Millbank bag. @ 100 gms
Vango Down Bag @ 850 gms Comfort 3C - Extreme -9C
Sil nylon ground sheet @ 90 gms
Thermarest Neoair short @250 gms
SOL Escape Bivvy @250 gms
Alpkit Carbon Walking Poles @300 gms
Sil Nylon Basha - Terra Nova Competition Tarp 1 @ 300gms
Bug head net. @50 gms
Alpkit Titanium Spoon and 10 tent pegs (i.e mix of MSR 7075 and Alpkit Ti)
Alpkit 1.4 Litre pot and frypan + Stainless Steel wood gas stove @ 400 gms
250ml Firedragon fuel. 250gms
Lighter, LMF cadet Ferro cerium striker and 20 BCB Windproof matches
Vargo Titanium 700ml Water bottle. @ 130 gms
Enzo Camper Knife @ 185 gms
Silky Pocketboy 170mm saw (without plastic case) 190 gms
2 days of food. @ 750 gms per day = 1500 gms (mostly freeze dried from Expedition Foods in the UK)
FAK @ 200 gms
Map and compass @225 gms
Tooth brush + Tooth Paste + Soap + microfibre towel @ 250 gms
Swingflex Solar Umbrella @ 230 gms

Total Weight is approx 9.5kg (21 lbs) with 2.65 litres of water

You may also want to take a Goretex Jacket and over trouser @ 600-700 gms