This year I saved a ton of money (like, at least $100) by ringing things up separately with the same coupons. It's great for big-ticket items when normally they'd only apply the discount to one single item! :)
All you have to do is tell the cashier, “Hey, ring these up separately so I can apply the coupon to both.” — Most of the time they won't even care, but the game is in your control, because you can always just come back and buy the other items later… and they know that, too.
The best case scenario is that they'll just be like, “Oh, we'll just give you the extra discount without having to split the transaction. It's no problem.” — But, of course make sure that they do before you leave the register! (…On your receipt, do the math! I had to go to returns to ask for a credit one time, but they were happy to give it to me.)
Shizzam! We were able to get the better models for my family because we lowered the price to that of the lesser ones… smart shopping. ;)