I hope everyone puts the oxygen tanks first!
(Did you hear about the first restaurant on the moon?
Good food, but no atmosphere)

And somewhere down the bottom would be your magnetic
compass (unless TMA 1 is what you are looking for)

Portable heater (you are already baking in the lunar day)

and

that Box ‘o Matches (unless you need to draw straws
on who gets to manually detonate the nuclear device to split
the asteroid in two and save the world, oops, wrong movie!)

Hope you rated that 20 liters of H2O second (it gets mighty
thirsty in those badland desert regions)

and speaking of the badlands, better rate the 45 calibers
somewhere up there too, could be good for discipline, not alien
encounters ("so tell me, do you feel lucky?" oh, not to be confused
with those match stick drawing episodes)

The star map is a keeper, sort of the lunar version of GPS (Tom Tom?)
and yes, signal flares I am told are self igniting by NASA and DO
work in oxygen free environs.

Yuck to dehydrated milk (duh, you need to use your water to
make moo juice?) and food? I have just 40 KM to go, remember?
Do marathon runners stop for a bite on the way? Those 2001
sandwiches looked pretty repulsive so food concentrate may be
wayyyyyy down the list too.

Now parachute silk and nylon rope (good for bundling up this stuff and dragging it along) and the SOLAR POWERED
RECEIVER TRANSMITTER better rate up there too, as well as the first aid kit and injection needles, which, yes, can be administered
without compromising your space suit, according to NASA

Where is the self inflating life raft? Did that get cut from the list?
Compressed CO2 instead? Hmmmm. Releasing some of that would
be a nice coolant; if my space suit was getting a little too warm in the daylight sun, that may be worth a shot!

I hope you never crash on the moon!
I pray this remains only an hypothetical exercise,

-y
~Psalm 23
References :

Single most useful thing you can have. The good news is gravity is low so you’ll actually be able to carry them.

2. Parachute silk

Portable shade.

3. Solar powered FM Reciever, transmitter

You might hear something useful and you can let your destination know you’re coming.

4. Nylon Rope, 50m

While not terribly useful, it will help in getting your friend out of that crater.

The rest is really, really useless and should be left at the crash site.

Matches – No firewood, no air in space.

Food Concentrate – You’d have to take off your helmet to eat.

Portable heater unit – The moon lacks wall sockets.

Two .45 caliber pistols – Sadly you won’t even be able to commit suicide with these. They’ll vacuum weld and the explosives won’t go off without oxygen.

Dehydrated milk, one case – More food you can’t eat.

Star map, moon constellations – Navigating by the stars is a good way to get lost.

Compressed CO2 – Unless you have some kind of jump jet this has no obvious purpose.

Magnetic Compass – The moon has no magnetic field. This is a paperweight.

20 litres of water – Wow, this would be nice if you could take off your helmet and if it was below the boiling point.

Signal flares – Stuff doesn’t burn on the moon.

First Aid Kits, Injection Needles – Because you’re going to inject your partner through his spacesuit? Or are you supposed to McGyver something involving the water or the CO2?

EDIT: Hmm, you learn something new every day. The flares would burn as would the gunpowder.

I still suspect the gun will vacuum weld.

http://en.wikipedia.org/wiki/Cold_welding
References :

Also, this is also one of those things that after you hand it in to your teacher, they are going to ask you for your reasoning. So if someone gave you a list with matches near the top, you’d probably feel silly for handing it in knowing that on the moon, those would be rather useless. Or would you rate the CO2 low, only to suddenly realize that maybe you can use it as a sort of propulsion system? Again, this really isn’t an exercise strangers can do for you.
References :

The compass is useless, since the Moon has no appreciable magnetic field. Same goes for the pistols, since there is nothing to shoot at, and in the absence of an atmosphere they would not be useful for signaling others.

Matches will not be useful either. Some matches may be able to burn in a vacuum, but what purpose would they serve? There’s nothing on the Moon worth setting fire to.

A portable heater will also not work well in a vacuum. You wouldn’t have much use for it anyway; if your spacesuit doesn’t provide temperature control, you’re not going to make it 40 km.

It will be very difficult to use injection needles, food concentrate, dehydrated milk, or water while wearing a spacesuit unless they are already inside the spacesuit.

The parachute will not be useful as a parachute (since there is no atmosphere) though depending on its color it might be useful for shade; I suppose you could also unfurl it and lay it out to signal a low-orbiting spacecraft.
References :