Plus, my son is so young, he doesn't need tickets to get into most places and he would have no concept that his grandmother bought him the tickets. I would be happy if she just bought him 1 or 2 meaningful pieces of clothes, rather than buying out the children's section of Dunne's Stores and shipping it over to me for an enormous amount of money.
Keep in mind that he doesn't understand she's bought him clothes either
In that case, I might have a conversation with her about your values. For us, we try to only use homemade, high quality things, or we buy second hand. We also have a very small amount of stuff now. We are trying to opt out of consumerism, primarily because of environmental reasons, but also because more stuff almost always equals more TIME SPENT SHOVELING stuff. And that takes time away from what really matters: our girls and each other.
Perhaps say something to the effect of: 'We really appreciate that you are trying to keep him clothed, but he really only needs about 10 outfits in each size, and we really don't have the space to store the rest. We'd also like to make a few purchases ourselves--this is our only chance to clothe this kid. Not that we don't like it, just that we would like to have some say, and to keep the clutter down.' You are welcome to steal some of my values for your argument, even if you don't share them

And don't worry too much, it took almost 5 years, but I've finally convinced everyone to stop buying my kids stuff.