My fav has to be my "bedroll", made up of a Thermarest inside a Softie Elite 3 grotbag which was all wrapped up in a TerraNova Jupiter bivi bag.
Last Friday night at 11pm I got to the Gap on the side of Crybin in the Brecon Beacons and the wind was howing! Within a minute the bivi was out and pegged in place and I was crawing into a warm slice of heaven. And for the rest of the night the wind blew and the rain fell and I didn't give a damn
As for what I have the most of it has to be rucksacks. Ranging from a cheap Wynster 25l through a number of Low Alpine and Berghaus 40 odd litre up to a Berghaus 70l.
At the end of the day you only need 1 knife or a couple of water bottles, but the things I use the most are the bedroll and the rucksack to carry all the "essential" kit. Without those everything else is pointless and a bloody pain in the lower back!