Wooden Armour and Heavy Wooden Shield
Druids have an unusual list of armour proficiencies as they cannot use any 'metal' armours:
Druids are proficient with light and medium armor but are prohibited
from wearing metal armor; thus, they may wear only padded, leather, or
hide armor. A druid may also wear wooden armor that has been altered
by the ironwood spell so that it functions as though it were steel.
Druids are proficient with shields (except tower shields) but must use
only wooden ones.
Note that as the description is in the original core rulebook and pre-dates the subsequent splatbooks. Therefore the list of available armours is actually much longer and now includes athers made of materials such as Stone, Wood or Dragon scales.
If all you want to do is maximise your starting AC quickly and cheaply then I would recommend the following armour and shields:
Wooden Armour
20gp for +3 AC is great and the downsides are minimal except for the hefty 25lbs of carrying capacity. If you can't afford the weight, then go with Leather Armour for a +2 AC bonus but only 15lbs of weight.
Alternative: Hide Armour
Dirt cheap at 15gp, it provides a +4 AC bonus in exchange for limiting your movement and your skills quite substantially.
The only reaswon I wouldn't recommend this initially is that having a 30ft movement is really handy! Being able to get out of trouble quickly is often more useful than an extra point of AC.
Light Wooden Shield
For a mere 3gp you also get a +1 AC shield bonus. There is no reason not to take this piece of equipment.
If you are wielding a weapon and a hevay shield then you cannot cast spells, but you can whilst using a light shield.