Any ideas on how to use leftover prime rib?

I love LucyS's suggestion...but you could utilize the remaining leftovers in a beef stew. Cook the basics for a stew first and add the already cooked beef into the stew for the last 20 mins. of cooking adding a ton of fresh herbs of different kinds of course. Delish!

Bim bim bap

Just plain cold roast beef is so delicious that I always just eat it up with a salad on the side and some baguette type bread.

I make thinly slices pieces w/ arugula in a steak sandwich for the beach.

Thai beef salad is a great way to use that up. Nice problem to have.

Another option, french dip sandwiches with au jus and horseradish sauce.

Philly cheese steaks "wit" or "witout" (onions). Don't forget the Cheese Wiz.

I would also say hash

Warm it up, slice thinly or cut into small chunks and add to a mixed greens salad with some blue cheese.

Prime rib makes the best Hash ever.

Make has or slice thinly for a decadent sandwich.

Tacos.