Not including cell phones, the biggest expense for me is a Pluralsight subscription, since my employer won't pay for training, travel, conferences, etc.. And I have to pay for the top of the line, which can be as much as $600. It is less if I catch it at a discount. I pay for the most expensive because Pluralsight offers an app I can use on my laptop so that I can download the training videos and watch off-line. This is necessary since the train I use to commute goes over areas where there's no connectivity.

Other than that pay for monitors, keyboards, mice as necessary. This has had the surprise effect that I've had to buy a keyboard for myself at work. They don't pay for good keyboards, since they don't pay for keyboards/nice/etc. I'm very envious of your employer, Steve Jones. If I didn't buy my own I'd have to use the 10 year old keyboards they buy. Those keyboards are like pounding concrete, so I buy my own.