I'm poor so none of this will probably work for you, but this is what I got my family.
Dad: $20 gift card for Tim Hortons. The guy is literally impossible to buy for as he doesn't have any hobbies. All he does is work.
Dad's Wife: A cooking book with slow cooker recipes as she's always cooking with it. Her kids I'm just giving them $5 in a card.
My grandmother: Boxed set of Downtown Abbey. It was on sale for like $20 this weekend and she loves that time period and is always looking for things to watch on her portable dvd player so I figured I would take a gamble and go with that. Only reason I know of the show is because of the guys talking about it a while back on the bombcast funnily enough. Also a box of Whoppers as she loves them and it's been a tradition that I get her a big box each year.
Aunts/uncles: One of my aunts loves chicken bone candies and like my grandmother is something I buy her each year. The other aunt/uncle I never know what to get so I bought a big box of ice tea mix and will give it to them as a double gift. No clue if they like ice tea or not, but who knows. And for my last aunt I'm giving her a box of that ice tea too, and I have been working on fixing her computer and am going to give her an old thumb drive I have had laying around because she wants to back up some photos of family that have passed away and she is afraid she will lose the pictures.
So you can take away from that, that when you don't know what to buy someone buy them a big old box of ice tea mix, a gift card, or do things for them that they don't know how to do themselves.