My alma mater, and perhaps yours, would like to take advantage of the concept of "Giving Tuesday" to get you to give them money. Here's some advice: Don't do it.
Send your money to a poor Kenyan or buy mosquito nets for West Africans in need. If you specifically want to help out an American, then walk out the door and give money to a homeless person on the street. If you want to help out with education, then find a local elementary or high school that's working effectively with poor kids and throw it some cash. There are a lot of things you could do with your charity dollar and essentially all of them are a better idea than giving money to Harvard or Yale or Stanford. For starters, though these highly selective charities like to talk about their generous financial aid policies the fact is that they rarely admit students from low-income families. And when they do admit students from low-income families, those kids usually already get a pretty generous financial aid package because these schools are already extremely rich.
The one and only valid reason to donate money to your selective and well-endowed alma mater is that you're implicitly trying to bribe them to give your own children preference in the admissions process. If that's what's motivating you, then by all means knock yourself out. Those legacy preferences are real, but they don't just exist to be nice. It's about getting money. But paying people to give your children preferential treatment isn't charity. It's more like anti-charity.