In my guide pack 1st aid kit I carry:
2 whacking great big dressings (military ones)
Duct tape to hold them on
Tick tweezers
Triangular bandage
Handful of smaller dressings
Steri-strips
Rubber gloves
Most of it's been used at one time or another.
I definitely agree with the above posts that antiseptic wipes and foil blankets are a waste of space. Minor cuts and grazes (that might want an antiseptic wipe) are best left until you're back at base as any dressing will just come off and/or the injury will get full of sweat/mud if you continue the ride. Foil blankets are useless in a mountain environment (especially a typically wet/windy UK one). What IS useful is to take the classic orange survival bag, cut it open (you'd never get a seriously injured casualty into one anyway), then duct tape a foil blanket onto it.
I also carry a SAM splint, I haven't made much use of it myself, but I have seen them used effectively.
The "if it's bad, call an ambulance" approach is all very well, but what if you don't have reception and it's going to take hours to reach a phone?