I haven't jumped to e5 yet, but last year I picked up a nice Humble Bundle. I can't use that content without the core books. I received a $5.00 gift card for Amazon and will probably start with the Handbook.
Of course, I'll need these the DM's Guide and the Monster Manual, too.
Is there anything else I should add to the list? Let me know in the comments below.
I could use this as an excuse to buy more dice.