Spartan Ops/Season One/Exodus/One Last Time/Walkthrough

The key to win this mission is how you manage your choice of weapon and ammo, because only very few are available.
Your load out: DMR, plasma pistol, active camo, plasma grenades, mobility (unlimited sprint), ammo
At the start of the mission, you will be facing an open end cave on the left and a passage on the right. Enter the cave, cloak on and start sniping from the open end. Start by sniping the elite (you have plasma pistol so go noob combo). Watch out the jackal sniper on the up ramp on the left(let's call this ramp #1). Once you take out the elites then head shot the jackal sniper (You would want his sniper rifle but if you drop him too early it will disappear). Once you thin out the herd, run to ramp #1 and exchange the plasma pistol with the covenant sniper rifle. You will notice there is another ramp and open end cave (let's call it ramp #2). Confirm there is no threat nearby (or just kill them all) and go to ramp #2, you will notice there is a weapon rack with 2 fuel rod gun. DO NOT TAKE IT YET !! 
Continue to the next area and you will see a few covis in front of the harvester. There are 2 elites (one with sword), some grunts and jackals, and a fuel rod grunt, plus a turret. Use the sniper rifle, head shot whatever on the turret, follow by the 2 elites, then the jackals. Try to stay away from the line of sight of the fuel rod grunt. So he will not fire at you and you will have more fuel rod gun ammo when you finally drop him. 
Once you take out all the enemies, go exchange the sniper rifle with the fuel rod gun. Hopefully it still have some ammo left because you will face 2 hunters inside the harvester. 
By now you should notice the challenge: Your DMR is running out of ammo, fuel rod gun only has a few rounds, but you will need some power weapon and some precision weapon, and there is none... 
Once inside the harvester, wait for the hunters to retreat back, then cloak on, move to the left, use your last DMR round to head shot the jackal sniper. This will alert the hunters so run back outside. 
At this point, your DMR should be completely dry. You can either take the risk, cloak on, and go back into the harvester. On the ledge on the left side (where the jackal sniper was), you can find a weapon rack with covenant carbine. Or you can run back to the ramp #1, where you will find a weapon rack with some useless storm rifles. I choose the second approach. 
I came back to the harvester with a storm rifle and fuel rod gun. Cloak on, try to get close to the grunts and take them out with the storm rifle. The key here is short control burst (Like in the movie Aliens). As soon as the hunters are alerted, run like hell, then come back and continue.
If your storm rifle is out of ammo, go back to restock. (And resist the temptation of taking the fuel rod gun).
Once the minions are out, then you can focus on the hunters. Hopefully your fuel rod guns still have a few rounds (it takes around 4 shots to drop a hunter). Start with the hunter on the left (so you can access the weapon rack on the ledge after you drop him).
Once you drop the first hunter. You should be able to get the covenant carbine (but your fuel rod run is dry). Get whatever weapon you can find and take on the second hunter. (I dropped the second hunter with nothing but a plasma grenade and a (few) useless storm rifles - yes I run back out to restock).
Once both hunters are down, move up and take out the few elites. Once the harvester is clear of enemy, you can insert the power supply and activate the laser.
The laser will dig a cave on the cliff. Enter the cave, move forward slowly, 2 promethean knights will appear, One on the circular ramp (has a binary rifle) and one at the bottom of the cave (has a scattershot and auto turret). Use peak and snipe to take out the one with binary rifle (it is more dangerous, one shot of binary rifle can kill you). Exchange whatever the non scoped weapon (like the storm rifle) with the binary rifle (you will need the binary rifle later so don't waste ammo here), take out the other knight with covenant carbine. Go back to the harvester to restock (yes you will do this many times in this mission), and go back to the bottom of the cave and move inward. 
A bunch of crawlers will appear, take them out accordingly. In the inner cave there is a Forerunner structure with a bunch of knight and crawlers, plus a watcher. Take out the watcher with the binary rifle (so nobody can be resurrected), then the crawlers with the covi carbine (you can tell which is which from the radar because crawlers move fast). If any knights approach, move back. After you clear out the crawlers, start taking on the knight with the binary rifle (head shot their face -> one shot one kill). Also, while scope in, take note of the weapon they carry. There is one knight with binary rifle and one with incineration cannon - try to leave them at the end so you can pick up the weapon before they disappear.
After you clear out all the knights, you will be told to go to the room below to flip a switch before the big door can be opened. Now is the time to check on your ammo because the room below has 2 knights and one of them has a binary rifle. If your binary rifle has more than 2 rounds, keep it. Otherwise, run all the way back out the cave. Restock your cavi carbine in the harvester and exchange the binary rifle with the (ta..da !!) FUEL...ROD...GUN (at ramp #2)
Assuming you keep the binary rifle (meaning you haven't take the fuel rod gun yet), go down the room below, 2 knights will be spawned. Take out the one on the right first (it has a binary rifle). After you take out the second knight, go grab the binary rifle dropped by the first knight. Check the ammo, you will need a few rounds because a bunch of covi will show up when you complete the objective and exiting the cave (including 3 cloaked angry sword elites). If you are not sure, like me, just get out of the cave now and back to ramp #2 to get the fuel rod gun (and stick with it).
IMPORTANT: If you take out these 2 knights with fuel rod gun, DO NOT exchange it with binary rifle - you won't have enough ammo for the covi at the end.
Once you are ready, flip the switch and exit the room. The big door at the platform above will be opened.
Before you go through the big door, check again your weapons, you should have full ammo for covi carbine and a power weapon that can take out 3 charging sword elites. (I prefer the fuel rod gun, save the best for last). After this point you will have NO ACCESS to other weapons.
Once inside the big room, flip another switch to deactivate the artifact. 
Objective accomplished. Now get out of the cave. Gravity fluctuation will throw you left and right (and up). While you approaching the outer cave, a few covis will show up, including those 3 (cloaked) angry sword elites, greet them with the fuel rod gun or the binary rifle. Then proceed to take out the rest with whatever weapons you have left.
Mission accomplished, now get out of the cave and board the Pelican.