There is a huge thread in wilderness & survival on this
I will post mine however, as its quite new and I'm quite pleased with it
I call it my pinstripe BOB. My kit had to be portable, inconspicuous, light weight and fit into a briefcase (i.e. suitable to take when I'm wearing a pinstripe suit

). Heres what I came up with.
1 6x Large tie wraps
2 Space blanket
3 'Utility'
Pencil with 2x 3ft pieces of duck tape and
1x3ft piece of PVC electrical tape
Disposable lighter
Small AM/ FM radio with earphones
Sharpie marker
Inova X5
SAK mountaineer
4 'Tools'
Stanley MAX Steel heavy duty pliers
Shark corp 8" tempered pry bar
Also LM squirt carried on person
5 First Aid Kit
Tissues
3x Burn Treatment
2x First aid dressings
2x Sterile gauze
1x Crepe bandage
1x Triangular bandage
1x Sticking plaster strip
2x Antiseptic wipe
8x Paracetamol
16x Puritabs
1x Sewing kit
1x Steri strip
1x CPR mouth shield
1x Perry whistle
1x Pair latex gloves
1x large freezer bag (water carrier)
25ft nylon cord
6 Clothes
Light weight quick drying t shirt
Also Kevlar gloves carried on person
7 Extra strong A4 size zip top folder to keep kit in
8 Food
Cereal bars (energy)
Liquorice (v. long shelf life)
I tried to choose things based on the possible situations I could find myself in. I also focused my FAK on dealing with serious injuries, and tools on things that wouldnt let me down or break.
If I had to point out weak points in this kit it would be
1. Lack of decent shoes, especially as I typically wear dress shoes for work. I cant help this however, I just cant carry another pair of shoes when I'm meeting customers. I have included sticking plaster to patch my feet up however.
2. Limited food/ water. Again I cant help this due to size/ weight limitation. If anything were to happen I would go to the nearest (safe) shop/ vending machine and buy bottled water and food.
3. Lack of a heavy duty kife. I cant help this as I live in the UK.