All of us approach wilderness survival from a different perspective. We all have different needs, different experience levels, and depending on where we live and when we venture outdoors, we'll all experience different potential challenges to our survival.
Just reading a blog post on the internet isn't going to make you a survival wizard, but we can hopefully help point you in the right direction to enhance your survival capability.
Assess your current skill level
Can you make a fire using naturally gathered materials, provided you have a lighter or matches? Do you know what materials to use for tinder and kindling, and where to find them? Can you find those materials the day after a heavy rain? Can you get a fire lit while you are still in the rain?
Do you know how to tie knots like the bowline or clove hitch? The age old expression of "if you don't know knots, tie lots!" works until you eat up half of your cordage trying to get a single lashing point to hold.
Do you know how to follow a compass bearing, and what unmistakable geographic landmarks surround the area you are in? If you ended up deep within the woods without a landmark to sight a bearing on, what direction could you safely travel in to follow a geographic feature back out to civilization? Is there a river you would know if you got to, a paved road, a mountain range, or a swap?
Hardware vs. Software
There's an adage in survival "the more you know, the less you need to carry". Point being, if you can improvise tools with natural resources, you don't necessarily need to bring them with you. The tools you bring with you should reflect the skill you have (or not!) with them. If you don't know how to setup snares for wild game, your snare wire is wasted space in your pack. If you don't know how to setup hasty shelters from natural resources, you better have good sheltering material with you at all times.
The items your bring with you should be there to conserve your time and energy/ calories. While you may know how to make a natural water container, or start a fire with a bow drill from natural materials, the time spent crafting those items would cost you far more in expended calories than carrying a 1oz mini-bic lighter, or a 3oz titanium cup.
The more software you have, the more you can get by with less. IE: getting sufficient firewood with a small knife and not needing a hatchet/saw, making sufficient shelter with a modest sized tarp versus a tent at 5 times the weight, cooking with gathered firewood instead of a stove that runs on fuel canisters that may run out.
Consequences and Probability
In general we can survive minutes without oxygen, hours without shelter, days without water, or weeks without food.
Depending on where you are in the world, and what season it is, these different needs may be easy or near impossible to meet in the wilderness. You need to plan accordingly for where you are going to be. A kayaker on a river, a hiker in the southwest, and a snowmobile rider in the northeast have different natural resources at their disposal; the kit they bring with them needs to reflect that.
What each of us need to survive 72 hours in the wilderness is going to be vastly different, and as a result, no prepackaged kit will be a "one size fits all". The confidence to use your tools under any foreseeable circumstance is paramount. If you don't know if you can get away without a tool (be it fuel soaked tinder, a hatchet or saw, a sleeping bag, or a tarp shelter) then you are best off carrying those items with you anywhere you might be stranded overnight.
Keep in mind though, the fire won't light itself and the tarp won't tie its own knots, and you don't want to be figuring it out for the first time after you fell into the icy water and your hands aren't working quite so well.
You must be honest with your ability level, and tailor your kit to reflect your current capability.
For further reading on the topics above we recommend the following resources:
Mountaineering: Freedom of the Hills by Moutaineers Books
Bushcraft by Mors Kochanski
Build the Perfect Bug Out Bag by Creek Stewart