Congrats on 36mpg! Every bit counts. And you're 17 bucks richer!
Until you get a gauge, here are a couple other ideas you can do without a gauge. You could easily turn off your car and coast your manual transmission up to red lights and down hills. Engine off coasting reduces city driving losses from stop/start. And at other times you could also use the car's deceleration fuel cut off function: slowing to lights or going downhill, shift into a gear that will put RPMs up to 1700 or 2000 and the computer cuts fuel to the injectors while you decelerate. I do it all the time on my 1998 civic now. My O2 sensor readings show zero voltage within a couple seconds, meaning no fuel or almost no fuel is being burned even though the engine is still "on." Saves brakes slightly too, I guess.
Good luck!