Must-have upgrades?

The first vanity upgrade should be the front DRL parking lights. An OEM harness and relay - plug and play, and the front amber turn signal indicators become DRL lights as soon as the engine is started. This is a $70 mod. This is the best way - don't waste time using relays or tapping into other wires.

And the fog light mod (use 14 gauge wire) - turn only the fogs and parking lights on. This is a $1 mod.

 

The one mod I apraisate the most is the led dome/map light loop ... where they come on at the same time when the doors open up ...
Not saying I don't apraisate the leather heated seats, auto start and all the other goodies just the interior led light mod been very helpful..

 

If you have a 2012-2015 the secondary air injection filter upgrade
One of my best pieces of advice I received before I bought my truck is the tailgate anti-theft mod. Gives me peace of mind when I park my truck in unfamiliar places.
Rear differential breather mod

All of these are cheap and easy.
I'm relatively new to Tacomas myself and I've been constantly adding upgrades/mods to my list.