The "ideal" mountain bivvy has cover from stonefall,avalanche,and has enough room to recline and sleep(the exception rather than the norm!).Heres a good tip,"never,ever pass an obvious bivvy site late in the day!".You will regret it! Much better to sacrifice a few hours of daylight and settle in for the night.The picture above has some of the gear i most prefer.
Use the climbing rope to set up a "clothesline" to secure yourself and your gear to the rock.Use the remaining rope to set out a "fixed rope" allong the next days ascent route(great move when your tired and stiff next morning).The clothing is superb-Full PARAMO(including TORRES duvet jacket in a compression sack)you can sleep fully clothed(wet or dry)and its like sleeping in silk! PHD-Zeta sleeping bag-1kilo,and good for 15deg below(more in full paramo!).JETBOIL stove for melting snow an ice with extra gas.You do not want to be lugging tons of water up with you when its there available! Harness stays on whilst sleeping attatched to clothesline by your "chickenchain",so as to be protected in and out of the bag.Simple polythene groundsheet under the small "THERMAREST" does for a mattress.As a "Bivvybag",a "BLIZZARD BAG" is used to encapsulate the sleeping bag this type can be used repeatedly and is great kit(if your only out for two nights,condensation is no big deal).The final item (not depicted)is a "TARP".I have been using a 3x3metre square of old Yacht Spinnaker,with shockcords tied in(3 per side)to anchor it to ledges.But now there are some realy great ones on the market!
PS:-Ime not getting any money for naming the above gear!?Its stuff that i use all the time because i know it works for me!! (Maybe the buggers should pay me?!)