Do anything that keeps your interest, show cases your skills, and demonstrates that you can learn on your own. Not knowing your interests or skills I can't tell you "Write such and such application using these Java and Python technologies."
Better yet get involved in an exist open-source project on source forge or some similar site. Doing that will also demonstrate your ability to work within a team environment as well as your ability to communicate effectively (at least in writing).
As well temper your statements about your skill level with some modesty. Having just over 15 years in this field, I can tell you that much of what determines if a person is a mid-level developer has to do with the following:
- The ability to create a reasonable design
- The ability to create maintainable code -- even for complicated situations
- The ability to communicate effectively within a team
- And demonstrate all of the above for usually about 3-5 years.
This is not a dig at newbie developers; it's just that no matter how smart you are, you can't gain the benefit of experience without having put in the time. There are intangibles that come with it, which you can't learn from a book.