Oh dear, you've got me started now, I'm a bit of a bivvy fan. I use a Rab Survival Zone bivvy, which is light ( about 350g ) and has stood up to 2 years of abuse. It has the disadvantage of having a drawcord closure rather than a zip, so in inclement weather you need to sleep on your front. Blacks down sleeping bag, light and cheap for a down bag. OMM duromat for mattress, this also folds to become the back support for the Classic 25L pack, saving weight and bulk. MSR Pocket Rocket stove and MSR Titan Kettle for cooking. Travel Tap for water purification, this fits nicely into a bottle cage. Other kit highlights include, Petzl Tikka XP headtorch, Berghaus Paclite overtrousers, OMM Kamleika waterproof Smock, Montane Litespeed jacket, Icebreaker Oasis crew tops, Endura Humvee shorts and a spare liner, Endura multi tights, an Ipod and as much dehydrated food as needed all packed up in Exped fold drybags. This stuff isn't for everyone, I've been lightweight backpacking for years and have gotten used to the discomfort that comes with most lightweight kit. Enjoy your bivvying, once tried you'll never look at a tent again.