The easiest way I have found is the following.

Say you have a category “Pies” with items numbered 1 to 4
1. Chicken pie, 2. Steak Pie, 3. Pork Pie, 4. Beef Pie

You first enter number 4 details, then number 3, then 2, then 1.

This will make your items appear on the menu card as 1,2,3,4, because WP puts the latest post at the top.

However, if you have already entered these details in a random fashion, you simply need to edit the post time for each item, using the above example with regards to the timing, this can be modified to the minute if required.

I hope this helps.