What a cool question, actually.
In my current situation? Probably a coffee date with someone new.
In a hypothetical "blank slate" scenario? Some easy way to play music. An mp3 player or something among those lines.
Alternatively - I could absolutely purchase a used dumb phone for that amount of money, as well as free calls within network for a year (in my country).
Just the chilled, filtered tapwater I carbonate at home.
Ludicrously cheap, the taste doesn't get old, and there's no trash to deal with. 10/10.