Lenses

A lens is the most important investment in Photography. Period.
While the electronic part of your picture taking device has to be replaced within 12-18 month because being outdated, your lens will last for 20++ years.

Please consider buying solid state of the art 24x36mm lenses instead of Tupperware labelled as "Digital".

Generally, avoid Zooms, Teleconverters and try to get f/2.8 or faster.