Fingers

Numbness of the fingers is a potentially dangerous symptom, often related to carpal tunnel syndrome.
This is one of many problems which can result from bad upper body posture.
The Two Bump Problem

Like your bottom, the heel of your hand has two bumps, with a sort of valley between.
There are important nerves which run through this valley, and it is important to avoid excessive pressure here. One common cause of excess pressure on this "valley" is riding on the top corners of drop bars in such a way that the bar presses here.
As with saddles, the "two bump problem" can actually be exacerbated by excessive padding! If you use thick foam handlebar grips, and/or gloves with too much foam/gel padding, the "bumps" that are best able to carry weight will press through the foam, but the foam in the middle will press back at the valley. Thus, as with saddles, too much foam/gel can worsen the problem it was intended to correct!
Wrist angle.

Numbness can also be related to poor wrist positioning. Generally, the wrist should be held so that the hand is pretty much in line with the forearm. If your hand is bent upward from the forearm, the nerves can get pinched, causing numbness.
Suspension, tire pressure