There are two areas this can be done in. Personally, I find one to be of more gain, but that's me. First, the area you start off in on the moon. Going from one side to the other back and forth over and over is certainly a good way to find chests, helium and farm kills. This also happens to be the location (under the tram in the big crater) where you can launch your sparrow up a wall like a vert and 'land' some 'tricks.' This is easiest with a timebreaker.. Next, the area to the right of the start. You can run circles en masse in this area for MASS amounts of helium and chests. They're EVERYWHERE here. Up the cliffs/hills, inside/atop buildings galore, and caves. There are also 2(3 I think) different kinds of public events that happen around here. When running the circle for materials, start at the solar panels on the hill and follow them to the circular region. There's usually 1 helium and 1 chest in this area alone. Sticking to the right, follow it along until you make your exit, still sticking the right wall. Make your way to the double caves, making sure to check ALL around for chests and helium here, including beneath the building. Proceed to the broken building in the center (and the broken connecting piece) as there's usually materials around here. Continue sticking the right and head into the next sub-area. Clear it! One more group of buildings, usually with at least 1 chest and helium, and your ready to rinse and repeat.