Being prepared for the apocalypse is not about purchases, it's about attitude and mindset, and knowledge and skills are not something you can go out and purchase. Either you live a prepared lifestyle or you don't and the learning starts now and doesn't stop
I know this sounds like a blow-off answer, but it isn't. It's like when people ask what to stock in a first aid kit. If you know how to perform first aid competently then you don't need to ask what to stock, you already know. If you don't know how to perform first aid competently then the best stocked kit isn't worth much.
Start by learning as much as you can about being self sufficient. The rest will follow.