They don't sell Canadian cigarettes at the duty free in Belize.
Otherwise, I agree . .they should just bring as many smokes as they think they'll need. Shouldn't be a problem at all, as long as it doesn't look like they've got enough to be selling them.

I should point out that if you are the type of people that easily make acquaintance of locals and have a generous nature, you'll probably need a few more cigarettes than you thought. Not that you'll be giving away packs of smokes or anything like that, but the single smokes seem to go pretty quickly on an evening out.