Obviously it's time to blow up the Forgotten Realms again.
But seriously, the first thing:
50th anniversary deluxe dice. In a fancy case. Two versions. One has the usual suite of dice (d20, d12, d10, d%, d8, d6, d4). The other is the masterpiece set, which has all the dice you'd ever need for 5e. It comes with 8d20 (two each of four colors, for four fighter attacks using advantage/disadvantage), 4d12 (for high-level poison spray), 5d10 (four for high-level cantrips, one as a d%), 4d8 (for high-level cantrips), 8d6 (for fireballs), and 5d4 (for magic missiles).