Tom Hamlin gives you a few ideas for the angler on your list.
First of all you can save a life if you pick up a life vest for your favorite angler. They make simple orange ones that are pretty affordable, or you can spend a little more money and get one that's lighter. Think about kids, they may like a bright colored life vest or maybe one that's based on a cartoon character.
One thing that's a little out of the ordinary is a boat seat. These can wear out and Tom says guys rarely think to replace them. You will have a lot of choices,so take a picture of your favorite angler's boat and make sure you know the make and model and then just go to your favorite outfitter and give them the specs.
Everyone can probably afford plastic tackle boxes. They are flat and come with plastic dividers that give your fisherman places to put in artificial lures. These run a few bucks a piece but Tom says this is what the pro's use and you can never have too many.