Depending on if you have them already, invest in a few tailored pieces clothing that go with a lot and you can wear regularly.
Offer to pay for your friends to come with you to do what you like (for instance if you like ice-skating and you all usually end up at bars, offer to pay for them to come ice-skating with you - they'll be happy to go for free, and you'll get better quality out of your time with them).
Give small amounts to charities you see along the street, if you identify with them (for the warm fuzzies).
Make a habit of buying something nice at a bakery or similar outside work once a week and bringing it in for your colleagues. Chat with them over it.
If you don't have dietary restrictions and are easy about what you eat, get one of those packages where they deliver you recipes and ingredients every week (cut down the time planning, buying and cooking and you can find one that's healthy and balanced - most are by design anyway).
Seconding spending more money on comfortable impressive looking clothing.
On ChrisHallquist's post extolling the virtues of money, the top comment is Eliezer pointing out the lack of concrete examples. Can anyone think of any? This is not just hypothetical: if I think your suggestion is good, I will try it (and report back on how it went)
I care about health, improving personal skills (particularly: programming, writing, people skills), gaining respect (particularly at work), and entertainment (these days: primarily books and computer games). If you think I should care about something else, feel free to suggest it.
I am early-twenties programmer living in San Francisco. In the interest of getting advice useful to more than one person, I'll omit further personal details.
Budget: $50/day
If your idea requires significant ongoing time commitment, that is a major negative.