I ran out of gas put 5 gallons of gas in the car drove car 2 miles. Filled it up. Went to eat. Then drove car 20 miles. Car sat overnight would not start next morning. Relay was changed. All fuses good. Still can't start car. What to do?

If this mini-van has an in-tank fuel pump, and you keep running the fuel at a low level, it will overheat and fail. I would caution you to keep the fuel level above 1/4 tank.

do you want to figure out how to figure yours out. a 20 year old car nothing is going to be average. to get it better lose some weight in the car. meaning don't carry 500 lbs of stuff you don't need. the less it weights the less the engine has to work which saves gas use. fill your tank normal till the pump shuts off and don't pull the handle to add more fuel. then write down the mileage. drive the car 200 miles. fill the tank again the same way. then figure out the miles you drove and how much gas you put in the tank. if you drove 200 miles and used 10 gallons you get 20 miles to the gallon. doing a tune up and checking your air in the tires can increase the mileage. good idea to check it first before doing the tune up to show it did some good. I did a tune up once and got almost 5 more miles to the gallon after

CKP sensor or cam sensor. one goes bad and causes other to go bad. easy fix and not too expensive.

You never leave a car running, as it will
overheat the Exhaust Converter
When you run out of fuel, you sometimes
ruin the Fuel Pump
It depends on gas to lubricate it,as strange as it sounds
Check fuel pressure & volume at the motor with a gauge

Sounds like an electrical issue. You'll want to take it in.

Well, how much gas did you put into it? 1 gallon or 5 gallons, or more?
electronic level sensors sometimes are a couple of gallons off.

could be your fuel filter gummed up from the old gas

Check the fuel filter, you may have clogged it when you filled the tank.

change fule filter if nothing changes do fule pressure test