These are some of the tips I can give from hiking and camping experience as well as RNLI and first aid training. Some of these are a bit emergency oriented, but we're not trying to be Bear Grylls here, are we. They are not really sound bite tips that belong in your list, but this seems the right place for them to be posted.
Just because you haven't used a piece of kit, doesn't mean you won't one day. Think about the IMPACT of not having it when you need it, no matter how small the RISK of needing it. Some people call me paranoid, but I prefer the term 'safe'.
Make sure you've got credit on your phone.
Always check the mobile network coverage for your area of travel and ensure that at least one member of your party will have signal at any time. Consider multiple network pay-as-you-go sims if your phone will accept them. Test them all before you leave. Maybe take two phones, especially if you're snap or text happy.
Put your mobile in a tiny dry bag. They cost about a pound.
Don't use your mobile to take loads of pictures, you'll kill the battery in no time.
There's nothing wrong with turning your mobile off to conserve battery.
If your phone has a GPS, learn how to use it in advance. Be careful of intense battery drain and use it only when necessary.
All batteries lose charge faster in the cold. Keep them and your mobile as close to your body as possible. It's a shame when your camera fails for that perfect picture, it's really annoying and impractical if your torch fails and it could be the difference between life and death if your phone doesn't work and someone's really hurt.
Try and get hold of a second mobile battery and ensure it's charged before you go.
Those emergency phone chargers might not look very bushcrafty, but they are invaluable in an emergency.
Check your first aid kit before you leave. The micropore tape might have gone sticky and someone might have had the paracetamol out of it.
Learn basic first aid. Since it's a little used skill, you might not remember it when you need it, so carry a waterproof first aid reference card in you kit.
Pain killers, stomach pills, anti-histamines, anti-diarrhoea & constipation, rehydration, blister remedy and tweezers don't all come in standard first aid kits but all belong in there.
Don't deny the ability of a tampon as a dressing, just because it's a tampon.
Bluetac makes a good temporary filling.
Burns go deep and keep burning, run your wound in cold water until it's freezing cold, not just until it feels a little better. Do this immediately. If it's tingling still, keep going.
The first rule of first aid and rescue is personal risk and the second is casualty risk. Don't become another casualty.
Know everyone's allergies, medication and important medical history and make sure everyone knows yours. Write them down and keep them on you. Always carry your important medication with you, never leave it at camp.
If you apply a tourniquet, write a great big T on the person's forehead and the time it was applied. You might not be in the ambulance (or helicopter) if the medic needs to know.
A survival bag is a bazillion times better than a foil blanket.
Wear your whistle, carry your first aid kit and keep your phone to hand. The last time I needed help I was upside down in a pile of dead branches and would not have been able to easily unpack my whistle from my tin in my rucksack, etc.
Know where you are, your colleagues are, your camp is, your car is and the nearest bit of civilisation is at all times. Distance and bearing FROM a known point is good, but not as good as a grid reference. Test each other as you walk.
Learn to read maps. Learn to work out where you are using your map and compass, assuming that you'd just teleported there. It's good fun to practice.
Home made plastic post-it arrows make great map markers.
Plan your long terms trip with respect to ending it early and how you'd achieve that. You may encounter bad weather, injury or just want to go home.
Don't over estimate how far you can walk. Have plenty of options PLANNED for early return to camp.
Don't only pack things you need most at the top and in the sides, pack things that are difficult to find in the dark there too.
Here's an exercise: Pack your kit one morning and try to find something specific in it that night, whilst wearing a blindfold. Don't just know where it is, actually get it to hand. Is the rest of your kit on the floor now? Can you repack it and not forget anything?
Don't get cold. Wrap up the instant you stop walking, hat included, not at the point you feel start feeling chilly.
Apply sun cream, wear a hat or cover yourself BEFORE you go pink!
Learn the symptoms of hypothermia, sun stroke, dehydration and for some of you, altitude sickness. Keep an eye on yourself and your companions, especially children.
You can get dehydrated in the middle of a cold night. If you're walking, keep drinking.
Prevention is better than cure.
Learn to spot inedible and poisonous plants as much as you learn the edible ones. Try to find a guide which illustrates fungi, say, which is edible along side the pictures of those which can be easily mistaken for it.
Carry a small (Collins Gem style) picture book on wild food. Books are better than memory. Think of the IMPACT of getting it wrong.
Know the sunrise, sunset, tide times, tide HEIGHTS, moon phase and weather, including cloud base and temperature at height for your whole trip. Try to get accurate daily weather reports if possible.
Carry a time piece of sorts, even if it's just your phone.
Always allow extra time for everything.
MP3 Players kill group moral, even if you're enjoying it.
Check in with loved ones. They worry, even if you don't.
Now for some lighter ones
A pocket planisphere is a good way of learning the stars.
A couple of note pages can be easily bound into a larger journal at home.
A pack of cards doesn't weigh very much. Learn lots of different patience games if you're on your own.
Dice are even lighter than cards and there are many games you can play verbally, most of which derive from drinking games.
Reward yourself for doing well. A shot from a hip flask of whiskey is a great reward.