Is there any way to estimate the total weight of the boat, motor, and trailer that I'm towing? I have a '95 Ranger 481VS (19'3'"), 150hp Merc, single axle trailer.

I can figure out weights of my gear and gas, but could use help on guess-timating the weight of everything else.

You could go to a truck stop that has a scale and do it there.  The one around here will do it for around $15.  That way you will know for sure what the exact weight is.

Your boat wieghs in at 1450 pounds.  You motor is +- 420 lbs.  Your trailer is probably at least 750 lbs.  Add 50-75 per battery, 30 for tmotor and 8 lbs per gallon of gasoline and you will be in the ball park.

Jig man is rigth on I'm  2900 lbs on a certified truck scale, zero tackle, zero gas, but with the 3 batteries , jackplate and trolling motor.  

30 gallons of gas  add 240lb + tackle

 You are very close to 3300lbs fully loaded.