Fixed bike bags are not good when going on the MTB, so I use a 45 liter HAGLÖFS lightweight backpack. I find it's easiest to remember everything when I think of it under the headings 'sleep, eat, live'.
A 3-season sleeping bag, a sleeping pad and a bivvy bag ought to do it.
My sleeping bag is stuffed in a waterproof bag and placed at the bottom of my backpack along with bivvy bag which is just rolled up. The pad is fastened with at strap on the backpack.
I've had a self inflating sleeping pad, but haveactually gone back to the ordinary type. The self-inflating is luxurious but unfortunately punctures often when one likes to rest close to the fire.
If you can light a fire it's just the best when you cook! To light my fire, I have some sawdust, a couple of firestarters, a spark stick, a small case with matches and striker, a lighter and a little sharp folding knife.
The knife can be used to make feather-sticks. When there are no dry twigs, dead birch bark or the like to start the fire with - the feather sticks are the solution (that's another instructable).
... But if all else fails I have a mini gas burner and a small gas can.
On a short trip I use a titanium kettle to cook. it works well - in a primitive way. You could eat directly from the kettle, but that's too primitive even for me ... so I have a folding cup and a titanium folding spoon.
For this short trip i plan for dinner, breakfast and little lunch the next day. Here I have chosen dried meat (like beef jerky), powdered mashed potatoes, onions and carrots for dinner. The dried meat is also for a small lunch the next day. And müesli to make porridge in the morning - with apple, raisins and dates it will be delicious. I have a total of 1.7 liters of water when starting the trip, but I plan to fill the bottles again along the way. I will use approx. 3 liters of drinking water for the ride.
I have also brought fishing gear. A 4-section spinning rod at 8 feet with a casting weight of 5-20g, a small reel with .22 nylon line, a pair of wire tippets (for the pike) and a box with various lures for lake and river fishing.
Often my favorite will be the tarp. You are close to nature, get all the fresh air you can pull into the lungs and you can be close to the fire. A tent is obviously nicer if the weather is bad or you are in an area with no trees or other shelter.
An extra line is good if the mounted guy lines are not enough.
I have no tent pegs with me - if I need some I'll make them at the campsite. The knot is a 'Siberian hitch'. It is especially good when it's cold because it is easy to tie wearing gloves.
When setting up camp it's good to have some tools: A good small ax, a folding saw and a good knife.
Now I'm almost ready to go...
I just need my puncture repair kit... and a pump, tire irons, folding tool, lights and the helmet ...And first aid!
When arrived I start to collect firewood and branches for pegs and poles for the tarp. When the tarp is rigged I light the fire. Then the camp is ready!
When you want to take a rest and it's cold outside, remember to use the sleeping bag. Even if you have the fire it may well be cold on the side facing away from the flames. Just remember to take off your shoes first ... Aaaahhhh, calm down, zzZZZZzzzZZZZZzzzzzz ...
Something that is good on the trips in cold weather are extra socks, mittens and hat to wear in camp. Here I have also a lower back piece of wool that warms if you're sore.
What to do out there
When the camp is set and all is ready you can go for a scout around, visit a nearby lake for fishing, take the binoculars and watch birds or other animals. The binoculars are also very good for watching the moon or stars at night.