If you use "2 pages per sheet" (in Page Setup) and set up a page as desired,
you can either duplicate the content on page 2 and then print the document,
or you can print pages 1, 1 to get the same page repeated on a single sheet.
Note that when you choose "2 pages per sheet," you need to change the page
orientation to Landscape to get two portrait pages on a landscape sheet.

Precisely. It took me a while to realize the potential of "2 pages per
sheet" in Page Setup, but one very useful thing it can do is make it dead
easy to print two 3" x 4" name badge inserts on a 4" x 6" card. Given that
(a) the inserts that come with Avery name badges are virtually impossible to
get right the first time and (b) we reuse the name badges and consequently
need new inserts, I find that doing it this way is the easiest. I print them
2-up and then cut them in half.

I had done the job in the past using 3" x 4" table cells, but of course Word
gripes about the margins, and it's a lot harder to reprint a single badge,
or to print, say, badges 2 and 3 (as opposed to 1 and 2 or 3 and 4) on a
single card. "2 pages per sheet" just makes it so simple.