If I won the lottery and had to spend it all in one day, I would donate to charitable causes, invest in real estate for long-term value, travel and experience new cultures, invest in education and personal development, support my family, and indulge in some luxuries and enjoyment.
pay off my student loans + any electronics i wanted to buy. also it doesnt specify that i can't transfer it into a different savings account so I'm gonna abuse the rules a bit.
My first purchase would be a first-class ticket around the world. I would visit every continent and see all the amazing people with all the beautiful cultures. I would learn history, cultures and languages, and just experience everything in the world that I can. I know it wouldn't be enough time to make it everywhere around the world, but I'd try my best. Then, I'd spend the rest on a giant cat rescue! I've always loved animals.