Most frugal way to buy items for a car?

This might be a weird question, but as someone who has to drive, I need to be prepared for an emergency and I want to know the most reliable, but lowest price way to get items for my car. I realistically need a personal pump that will inflate my tires; Along with that, however, I'd want an emergency road kit. If someone knows where I can buy oil in bulk for low relative cost, I'd love it.

Thank you!