2003 Honda Accord (4cyl auto) in good shape, runs well, about 24000
miles. No maintenance on the car except oil changes and did one about
1000 miles ago. Front tires are replaced recently (back tires look
very good) so they are almost new condition but I'm not getting the
mileage I did on the highway. Once with a full load (4 passengers and
luggage) got around 37 mpg (mileage then was about 12,000 miles) and
about a month ago (same trip, mileage around 22,000 miles, less load)
got around 32 mpg and now for the same trip, I'm guessing a bit less
than that with less load. I'm guessing 27 to 29 mpg (I didn't fill
up yet). I drove it locally a little (35 miles) before taking to the
highway (300 miles) so I expect less than 37 but 27+ sounds a bit
severe. What do you guys normally expect to get on the highway for
this car?

I realize traffic, weather, load and speed have some bearing but just
so I don't overlook the obvious, what are the "simple" things to check
that I can replace and help improve the mileage? Off the top of my
head is the air filter. I'm not sure about the pcv valve or fuel
filter for mpg since the car runs well as far as I can tell otherwise.
I hate to mess with the engine more than I have to because I'm a bit
hesitant since I haven't done these type repairs in years and I never
worked on this car so the placement of things is kinda new to me.
Around town, it still averages around 24mpg which seems to be fairly
consistent since it was new. thanks