What should I buy first

Olivia • Mommy to Isabella❤️👑
So I'm 17 and almost 12 weeks pregnant, I'm not sure when to start shopping, what are the first things I should buy, and not sure how much I should spend, I don't want to be over spending or not spending enough, I'm not gonna be doing a registry cause I don't really understand how it works and I don't find it necessary, but I will be having a baby shower later on in my pregnancy, I'm just wondering when did all u star shopping and what were the first things u bought for the baby, I'm young and a first time mom so I have these kinda questions haha