1. A good editing program such as
The Gimp which is free.
2. A good understanding of your camera and how to use it, which could be accomplished through books or through reading websites. Understanding Exposure is often recommended, but also reading about composition is also an important aspect.
3. Patience and a good attitude towards the fact that not every shot is going to be perfect every time (free, but damn hard to have
)
4. Lots of memory cards & a 50mm lens are always really useful to have and both are affordable.
5. A desire to try new things and build gear to try out (DIY is a lot cheaper and lots of fun and can be used for lots of things
)