I struggle with my mother with gifts as well - she can't help herself, she loves buying and giving gifts for me, especially as she can get them at a bargain in her country, which makes me feel terrible because they are never things I want or need, for example, clothes that are too small, fancy unnecessary gadgets - she bought us a selfie stick twice even though I told her we didn't need it the first time. She brings them in big suitcases from abroad and barely remembers what she buys. It's part of her culture, gift-giving when you visit someone, so I can't avail her if it completely. I've begged her off, saying I won't use or wear it, we don't have space, so she's cut it down, but she can't stop herself completely. When we had our baby recently she bought us a sling from groupon. It was a nice gesture, but it was from a Chinese company I'd never heard of, and apart from safety reasons, she would be depriving us of choosing something so personal for ourselves. This amongst toys and clothes years too old for baby (we really, really don't have the space), all brought from overseas so it can't be returned.
It's such a terrible waste of money and resources and we are big believers in reducing waste and trying to get everything secondhand. We had been hoping to rely on her generosity to alleviate some of the financial costs of stuff we have to get that is new or expensive, but have ended up buying everything ourselves. I've just learned to put up with it, express gratitude and then give it all to charity. Buying gives her so much pleasure, and it will benefit charity shops and other people more.
So OP, I do understand where you're coming from - I think all you can do is try to point people in the direction of things you really need, but express gratitude anyway if you are given gifts you don't want, give them away and remember that they will bring a lot of joy to other people.