A clipper set for haircuts. I keep pretty simple haircut and being able to do it myself saves a lot of time as well as money.

I'm a little late to this post but a Wahl haircut kit for $23 is awesome, even if you're just going to trim the edges in between haircuts:

https://www.amazon.com/dp/B0026IBSVE/ref=cm_sw_r_cp_awd_Otm-wbEJ5JXNE