You know what's a big bummer? Opening presents Christmas day and realizing that the amazing toy your kiddo has been waiting for all.year.long needs batteries you don't have on hand. Also a bummer: Realizing that there is absolutely no stores open on Christmas day to go get those batteries. 
So, here's a mom tip for you: Buy those batteries now, instead of waiting.
Pick up a few packages of Rayovac batteries when you're out Christmas shopping and either put them in the stockings or in the gift packages themselves. It may not be the most exciting thing they receive that morning, but a stocking stuffed with batteries is certainly better then possibly forgetting to pick up any at all and seeing disappointed faces come Christmas morning.