First, he'll eat it if he's hungry.
Second, don't start pampering him because you'll be sorry down the road.
Third, make a list of what he likes to eat and go from that.
And Joe's got a great idea - if he makes his own sandwich, he'll be likely to eat it.
Also, maybe he doesn't have a big appetite.
Maybe change the sandwich up with a piece of leftover pizza or something leftover that can be eaten cold.
Are you giving him juice boxes?
Have you asked him what he'd like for lunch?