As far as the soda cards (for kids), they are cheaper to purchase the day you arrive on the ship (are $14.95, I believe). You can buy them at the Information desk. Whereas if you wait until the second day, it is $19.95. I just returned from the Carnival Triumph (yesterday).
jeff as far as the drink coupons you need to buy them before you sail they cost 19.50 for 4 coupons. we sail in oct. and they saved us some cash .it cost 3.75+15% tip for a good mixed drink and 4.75+15 % tip for a frozen drink it is alot cheaper to use coupons.plus you do not have to take out you sail&sign card or sign for drinks you just give them your coupon.