My ds stopped napping at 16 months which sounds like a bit of a PITA, but would then sleep for 14 hours at night which was lovely and I wouldn't have swapped back. It's probably mad to consider your ds stopping naps as the hour you get free in the afternoon may be really useful when you have a newborn, however it is worth considering if, 1- he doesn't go down easily anyway, 2- he will be so tired at night he may go down a fair bit earlier, and may sleep a good few hours extra?
Find a nice small box, cover it in lovely boy's wrapping paper, wrap the lid separate, and fill it with nice useful things; a book (new one to him, try charity shops as you may need a few!) a tiny new toy like from a party bag or similar, maybe a new pair of pants or swim nappy, dvd that's been hanging around and he hasn't seen, a photo of something new to talk about, just anything he has never seen bafore and this may keep him amused for well, who knows. I thought of this for feeding times when dd was born, ds was 2.9 but fortunately didn't have to. The list is endless, and you needn't spend much. Buy a multibag of mini jammy dodgers, they always go down well. Bubbles? A magazine? Save the toy separately before he sees it for another time. Yes they are rubbish plastic that brakes but hey if he's never seen it before.....you get my drift. Try the psrty bag isles in supermarkets, try www.hawkin.com for stocking fillers. Cartons of juice, chopped fruit.
Walk the legs off him to get him tired (though you will probably be more tired!), and lots and lots of positive attention will also help! Good luck!