Night nav is a different ballgame indeed.
A lot of it is getting used to walking in the dark over rough ground (using a white light all the time is counterproductive as it creates shadows, kills your night vision and people get a bit worried when they see lights on the hill late at night) and having really good navigational skills.
On a clear night, you'd be able to use everything from celestial navigation through to random streetlamps as an aid to keeping on track, but sod's law states that it will be on a night with thick fog and no moon and so you'd be limited to the mainstays of micronavigation - things like walking on bearings, pacing, routecards, handrailing, off-pointing and all of this stuff that most of the day-walking community are kind of unfamiliar with, and when tired, hypoglycaemic, dehydrated and wet at last light call the MR team out as a result of being "lost" out of lack of confidence in their skills.
As for head-torches, if you've got the dosh, I'd recommend a Silva L1 for main use as it has really long battery life and a good beam, but I have some reservations about its watertightness (mine failed halfway through a stretcher evacuation at 0230h in drizzle!) so a backup is a good idea.
I never understand why people just say "spare batteries" when your torch with 300h battery life can fail for so many other reasons, leaving you fumbling around for AAs in the dark which may not fix it, so I prefer a wee tiny little Petzl E+Lite which weighs a few grams and gives a good enough beam (mine survived the washing machine)
If you're really keen on your nav, a third
torch, a small penlight (e.g. mini maglite/solitaire) with duct tape over much of the lens is worthwhile, so you can look at your map without killing your night vision and making relating the detail of the map to ground really difficult.
You can get torches with colour filters to prevent exposure to white light, which is worse for night vision. These are best left to the forces though as they have the disadvantage of making contours on OS maps (red light) or forestry blocks (green) or water features (blue light) much harder to see.
If you were doing this in a group, reflective panels on rucksacks is a good idea. Nite-Ize flog a dayglo/fluorescent panel with an LED in it for about £15 which you could hitch on your rucksack. It reduces the chance of getting seperated, and if you were in bad vis or featureless terrain, you could put your partner out in front and use him/her to take a bearing off and reduce "tracking" off-course.
A couple of glowsticks make a handy addition to your emergency bag too. Some of them come with a length of string which you can tie the stick to and spin around. This makes them useful to attract the attention of someone at great distance in emergency, and looks spectacular through night vision goggles.
I MUST take a bivvy bag no matter what,
A lot of people doing this start out after an overnight bivvy just beneath the summit of Snowdon, don't they?
Which means you'd have a bivvy bag and sleeping bag anyway. One of those orange bags of doom is a desperately uncomfortable way to spend a night, so if you couldn't take a bivvy bag/sleeping bag combo, one of those shiny silver blizzard bags would be a good prospect. I've trialled both as treatments for hypothermia and find them a second compared to a good sleeping bag, but they come vacuum packed and weigh very little.
There's a very good case for having the ability to bivvy up on any hill trip anyway.
as the one of folk he went with hyperglycemed and just fell asleep as she walked so that they had to get her wrapped up warm until she could be rescued.
Hypoglycaemia (low blood sugar) is more likely than hyper, which is specific to diabetics. Hypo can occur in anyone who is tabbing along in the hills without maintaining a good, steady input of fuel.
The likely outcome of the above is MR medic pitches up, rubs something called hypo-stop (a glucose gel that diabetics use, or perhaps a glucose drip if the casualty was deeply unresponsive) on the casualty's gums, casualty starts responding, gets more hypostop and starts getting with the programme. Perhaps the rest of group gets a gentle lecture.
If it was hypo, the whole situation could have been prevented by recognizing the signs before the poor person passed out (usually a lack of energy, confusion, aggression, inability to square away their admin - a lot like hypothermia really, and both conditions go hand in hand in the hills) and giving sugary food or drink.
Better still, a top tip is to be frequently snacking while walking, or at least the first sign of tiredness or difficulty navigating. Guys on selection for special forces often have an ammunition pouch full of jelly babies which they graze from as needed. The idea is transferrable to the vegan hillwalker. You can get vegan jelly babies and sweets, or chocolate cut up into bite-size squares and put a pouch full on the hipbelt of your rucksack or in a ziplock bag in your pocket.
I had some experience with this a couple of years back. I was out on the hill with an Army officer with the mentality of "I'm harder than this hill", bless her. She didn't admin her layers properly, and had a huge packed lunch rather than frequent nibbles. So after a couple of hours she felt really cold and grumpy, early stages of hypothermia were setting in while the rest of the group enjoyed the no-vis views.
Once we spotted this we put my warm layer and a mate's duvet jacket on her and filled her face with jelly babies. Problem solved - got her up and moving in a few minutes, and kept her moving and fed for the rest of the day until we got to the pub.