As an older sister, I would say....don't *always* go the route of buying them both gifts. My sister used to get a gift on my birthday! (sigh, still a bit bothered by that apparently) as my parents didn't want her to feel "left out". Now I know that it was partially because she was totally prepared to have a screaming meltdown if she didn't get one, but *then* it made me feel a little sad that I wasn't...special for at least a day? And the whole I wasn't allowed to have my own whatever until X age, but my sister could get one when I did? Yeah, didn't fly so well. I stopped asking for things and just saved up to buy them on my own, although sometimes she still managed to get them bought for her. (She's a nice person! My parents were just overly focused on "being fair" while I was growing up!)
I think it's great when you're bringing something back from a fun trip to ask what everyone wants. But, as a kid, I wish my parents had been willing to let us have the fight or whatever instead of constantly trying to appease/avoid it. I had a great babysitter who, when we were being whiny about not being "fair", would tell us "fair isn't equal", which is something that really resonates with me. It will all even out in the long run!