just remember the rule of 3in shtf situations)
3 minutes without air
3 hours without shelter
3 days without water
3 weeks without food.
With this in mind go to the dollar store and buy anything that could make getting any of the above easier.
Once you have these then you can start getting things that will make life easier post shft.
allot of the stuff you will need can be found around the house. E.G 2l drink bottles for water storage, plasters and pain killers for a first aid kit.
As for the family thing, they might one day come around to the idea( i doubt my family ever will though) but once they see that it is not just a phase you are going though, they should accept it.
Join your local army cadets (or the american equivalent), yes i know it's not the coolest thing in the world but the skills they teach you will be invaluable.
and lastly read this book: SAS Survival Guide: How to survive in the Wild, on Land or Sea (Collins Gem). it has been a massive help, teaching me how to catch food, what is the best food to catch in different environments, eatable plants, safe fire starting, shelter building and lots more.
If you have any questions or just want to chat with another teen preper just send me a message.