When you say you need to survive for 24-30 hours, you mean overnight. You assume that you will stay warm by building a fire. OK if below timber - not so if above timber. Or if you are hurt, gathering wood may not be possible. Here is what I take on a day climb in the Wind Rivers - similar to Big Horns.

1) Waterproof outer layer - rain jacket with hood and rain pants
2) extra insulating layer - 200 fleece or equivelent wool top
3) wool or wind-pro hat or balaclava
4) extra pair wool socks
5) day pack - long enough to stuff my feet in up to my knees
6) reflective metallic type mylar survival blanket
7) small 2 ft x 3 ft ensolite pad to sit on - doubles as backpad in my daypack
8) 2 trail bars, 2 sticks of cheese
9) first aid - similar to yours
10) maps ( I do not use a compass in areas I know well)
11) fire starters - REI waterproof matches
12) water bottle - 1 qt. old vinegar bottle
13) down vest in spring or fall when nights are colder

I have spent a few nights out on climbs with this gear and survived but did not get much sleep. This stuff will not fit in a hip pack. I personally favor extra clothing over depending on being able to start and keep a fire going.

I am sure I left of a few things - did this list off the top of my head. I honestly have never used a knife in a bivouac situation. Best other item - a warm partner. Spending a night out without bag or tent is easier when lots of bodies huddle together.