Below are survival items listed in order of The Survival Three's: Air, Shelter, Water, Food. Pick one item from each group. You may not prefer one from my list but they are examples of what you should get to take your first step to being better prepared and adaptable.
The principle you should use when choosing your basis is "nothing too expensive to start with, and keep everything small enough to all fit in a backpack with room to spare for a change of clothes". This not to what you would get to go camping, but what you need to survive in the worst-case scenario. Once you have the basics, then you can fill in more as you get comfortable with the idea, but you should try and keep it as light and minimal as possible.
3 Minutes Without Air
3 Hours Without Shelter
3 Days Without Water
3 Weeks Without Food
Instead of trying to store 3 weeks of food, for the purpose of the basics, you want to be able to boil water to cook food. Boiling water also makes it safe to drink and can keep you warm as well. You can also fit a small camp stove and some gas in the Stanly cup as well. Instead of picking one of each below you should get all three or something very similar.
These are other items that are essential to survival and should also fit easily inside a backpack.