Get yourself a super-cute swimsuit. Perfect for water parks, reading by the beach, or lounging by the pool! My favorite retro-inspired swimwear is usually found at ModCloth, but treat yourself to any suit that makes you feel great.
Learn more about the Quantified Self movement. From last.fm to Goodreads, I've always been obsessed with tracking my activities. I stumbled upon Exist.io, a service that connects a variety of tracking tools to find correlations, and I signed up as soon as I could. Too cool! Try self-tracking yourself to see if it leads to any interesting correlations.
Invest in your hobby. What would take your hobby to the next level? Taking a class or online workshop on a new technique? Buying new equipment to make mundane tasks go by quickly? Allow yourself to make the investment. It's totally worth it if you do that activity often enough!