I like the hand crank fuel pump so you can count the number of cranks and monitor fuel consumption.

I like the glow drivers with the replaceable battery AND the meter.

A (cordless) electric starter is really nice to have, but I got away for a whole summer without one. I now have one with a pair of 6cell rc car battery packs =)

Alternative to the above two is a 12v battery and power panel, and run you stuff off of that. Maybe you knew that or already have one for chargers?

After run oil is debatable, but if you ask BAX in the OS forum, he says ALWAYS use it, regardless of the fuel label says. I use it.

Clean towels, cleaner to clean off your plane (windshield washer with a heavy squirt of dish soap works very well) in a spray bottle.

Extr glow plugs (2 or 3?)