This is super simple, but I've run it a bunch of times during NH5's "What would you like?" unit and it's surprisingly effective for practicing numbers.
Give each student a small piece of paper or a whiteboard. Have them each write a 3-digit price (i.e. "360 yen", "250 yen") on the front, and their names on the back. Have the students walk around holding their cards/boards. When two students bump into each other, they show each other their cards and quiz each other on the numbers, like so:
A (holding up "360 yen" card): How much is it?
B: It's...360 yen!
A: That's right!
B (holding up "250 yen" card): How much is it?
A: It's 250 yen!!
B: That's right!
Once both students have successfully read the numbers, they then exchange cards/boards and go find a new partner. The goal is to exchange cards as many times as possible with as many classmates as possible in the time provided, so they're exposed to a ton of different numbers. It's also fun to see where your own card ends up.
Once you've run this one, you can re-use it as a very quick warmup. You can also run it in multiple rounds and build up to more complex numbers by starting with just hundreds (200, 400), then having them add a tens place in the next round. Level up!