I'm getting an SMS and a GG for Christmas... Anything I need to know?

My knowledge on these two systems is fairly limited... I know the SMS is region free (At least between the US and Europe) and it plays cartridges AND cards, and I know that the Game Gear drains batteries like there's no tomorrow (So I'm getting a wall cord for it, or whatever you call it, to use instead of batteries). I know the Game Gear screen is kind of small, and I know the SMS can also use Genesis controllers.
But is there anything important I don't know (i.e. "Sometimes you have to twist the plug in a 180 degree circle to get it to work")? I only know about the NES on up. Any help, even if you think it's stupid, would be appreciated. What might seem stupid or simple to you may be something I don't know.
Thanks for your help!

If it hasn't been done already make sure you get the Game Gear's capacitors replaced. The ones Sega used at the time were notoriously bad quality and in most units they'll either be dead or on their last legs. You want them out of there before they leak and cause damage.

Also, if you have a model 1 Mega Drive or Genesis you can use its power adaptor with the Game Gear.