I use a Lowepro Whistler BP 450 AW backpack for my 4x5 kit. It can fit:
Linhof Technikardan S45
Standard bellows and bag bellows (each in a padded wrap)
Large, waterproof dark cloth (Paramo)
5 to 6 lenses, ranging from 72mm to 450mm
Lee bellows lens hood/filter system + various filters
Cable releases, stopwatch, spare batteries, loupe, field notebook, small torch
Sekonic L-758D meter
1.5L water bottle
Tripod
12 x Toyo double film holders (in two Photobackpacker cascading wallets)
Linhof Techno Rollex 6x12 rollfilm back
I haven't actually weighed the pack thusly loaded, but it is damn heavy and not all that comfortable if I'm being honest. It's tough and well made though.