I tend to use 2 for most purposes, I think.

2.

It depends on how hammy you want your sandwich

uses two Quorns.

2

for me, one slice feels like you're cheating yourself; two feels a little luxurious; three feels gluttonish.

Usually two.

I ask, because I recently saw a pack of sliced ham, about a pound, and about maybe 50 slices, with the message "makes seven sandwiches". And I thought... what KIND of sandwich are we talking here?

apparently some people put LOADS of ham in their sammich. Googling "ham sandwich" photos, shows me this is common, at least if they plan to take a photo.

But it seems I know none of these sandwich-stuffers. All my friends seem to be two-slice cheapskates. I'm in good company, then.

But I confess, if I am toasting the sammich, I sometimes take a third slice, wrap it around some cheese, and toast that separately. Because I need something to nom on while I cut my sammich. Or something.

Depends on the thickness of the slices for me. I use as few as two if it's bologna-thick (Though I hate bologna), and as many as ten if it's sliver-sliced.

(Such as the Buddig packets.)

the suppliers are trying to seel more ham by suggesting you need umpteen slices per sandwich.

sell

noticed this behaviour in the USA. I tend to think of it as "greed".