I'm wondering what I can do to a 16v 1.6 to get better gas mileage.
Did a search but thought I would also pose the question to everyone.

    Less right pedal.Just kidding.Some of the "POWER CHIPS" and "MILEAGE ENHANCERS" actualy work.
   Also keeping it well tuned and tires properly inflated will make a big difference.

Hi flow Header and 2-2 1/2" exhaust, tires at 32psi. Get rid of extra weight, air filter, plugs, etc. I'm shopping for header and exhaust, I've heard reports of +- 5 mpg gains + better excelleration. I'm getting about 26 mpg with 16V and 30" tires, hoping for more.

Exhaust helps a lot. 5mpg from stock would not be out of the question. You will get the most "bang" for your buck by adressing the stock muffler and converter. Most of the back pressure comes from the muffler, so you will see the biggest gains by swithing to a welded turbo muffler or a dual-chambered bullet muffler. Straight-through exhuasts like glasspacks or no muffler at all help high RPM performance, but can actually hurt low-end.
In the 12 years that I have been in the exhaust biz, almost every Samurai/Tracker/Sidekick that I have seen has a converter that is at least partially melted-down. This hurts MPG! I would switch to a high-flow performance converter in a 2"(2 1/4" at the most). These are made to be used on modified V-8s over 300 cubic inches, so there is no way the 1.3/1.6 will blow it out or melt it down! You can even get them with O2 ports for OBDII vehicles.
Headers are another mod that mostly helps at high RPM's, but they don't make much difference during normal driving conditions. The only advantage would be if you wanted to build a full custom exhaust from the motor back out of large diameter pipe, the larger collecter diameter would make it easier. This would be big $$$ though, and would take a while to pay for itself in fuel economy gains. Headers are also high-mainenance. They leak, warp, crack, eat gaskets, and have to constantly be re-torqued!

K&N air filter helps too...

Check out this sight for a low-tech spark plug upgrade that is supposed to help:

http://performanceunlimited.com/documents/plugsidegapping.html

you could stop driving it,  and ride a bike to work.   the it wouldn't matter.... fix the symptom not the problem.

I've been running prolong in my oil and gas for about twenty years, it helps about 8 mpg on my 16 valve engines and alot more power, it's about twenty bucks at napa for the two pack (gas and oil treatment)and I run the bosch plus twos plugs and the k&n filter, my wifes four door gets 33 mpg on good gas and about 30 with the crap gas. oh ya auto trans.

When I first got my 92 4 door, I was getting 24-26 MPG.
I swapped on a header (rest of the exhaust is still stock), tune up (plugs, wires, cap, rotor), removed the airbox and put a K&N type filter on the end, went from 215/70 tires on steel wheels to 225/75 tires on aluminum wheels, and now it will get 27-29 MPG (yes, that is adjusted for the change in tire size).
Like was mentioned before....you can spend a lot of $$$ trying to pick up a couple of MPG...you have to figure how much it will cost and how long it will take for all the mods to pay for themselves in gas savings.  More than likely, you will never break even, unless you get really good deals on the parts/pieces; or the reason for getting poor MPG now is because some part is faulty causing the poor MPG and by changing it out you will pick up substantially more than a couple of MPG.

The biggest issue woth my '96 is tire pressure.  Those helpful guys at the oil change place like to make sure it is set to factory specs...   ...23psi.  As a result it gets about 24MPG.  Just pumping the tires up to 32psi gets the mileage up to about 29MPG.  It rides like a brick, but it's worth it...