Help needed in choosing my 4th card ever!

Hello kind folks,

I’m a 23M grad student looking to get into the credit card game.

I have had the basic discover card for about 2 years now with a 4250$ limit now. Don’t really use it much except for the occasional Walmart run.

It’s been a year since I got the Amex blue cash everyday and now my limit is 11500$. This is my main expenditure card.

And it’s been more than 6 months since I got my Chase Freedom Unlimited card. Limit is close to 5000$. This is my main Costco card as it is Visa!

I pay all my bills at the end of every month (1500$~ expenditure) and my FICO experian credit score is 735.

How can I up my credit game as I probably will have a few new expenses coming up? (Phone, laptop for the next 5 years, or maybe even a flight ticket that costs close to 2000$)

My annual income is about 27000$. And I’m also an Amazon Prime member though I don’t order bigger purchases from there.

Please advise me and thank you again in advance!