What to use Elerium Cores on

[halo_xe]

New to the game. I take it that these particular items/resources are rare? I just unlocked access to WAR power armor and another variant (Psionic I think?), and was wondering if either of these are worth spending a Core on. I already have one E.X.O. suit and one Spider suit. If they arent worth spending a Core on, what should I be using them for preferably?

[Coyote]

Yes exosuits are great.
Also, if you built a proving ground you can use a core to research ammo types and grenades and other such stuff and get a random unique weapon/item each time.

[Mimic Bait]

eventually you will be able to disect mutons and unlock plasma grenades in the proving ground, research that as soon as possible because they replace frag grenades

[Kiyohime]

experimental ammos
experimental grenades
experimental heavy weapons (late game)

[HeyRomo]

By the time i unlock WAR and Wraith suits by finishing Powered Armor research i'm usually closing in on the late game and have used cores to make nearly everything i need...so IDK what you have already used cores to make.

WAR and WRAITH are upgrades to EXO and Spider suits.
WAR suit unlocks Experimental Powered Weapons - these are good. So i build a WAR suit and then spend cores to get Blaster Launchers and Shredstorm Cannons.

[Cahos Rahne Veloza]

SPARKS also cost 2 Elerium cores to craft each.

[Mimic Bait]

Originally posted by Cahos Rahne Veloza:

SPARKS also cost 2 Elerium cores to craft each.

that explains how I suddenly had no elerium cores once

[JaegerBane]

For some reason, my last run had me swimming in cores, first time I've ever had enough to research everything I wanted.

In general, over a full campaign, I try to get:

2x EXO suits
1x Spider Suit

2x Wraith Suits
2x WAR Suits

1x AP Ammo
1x Talon Ammo
1x Dragon Rounds
1x Tracers

2x Blaster Launcher
1x Shredstorm Cannon

1x Acid Grenade

1x extra SPARK

Meaning I need 16 cores overall to get the minimum set of gear I prefer to use across the run. Once I've satisfied that then I start throwing cores down for extras. I'm not above reloading if I don't get what I want from the Proving Ground projects because, to be honest, I've yet to hear a good explanation as to why it's a random result in the first place and having to gamble a resource that itself is a gamble to acquire is just a plain derp design flaw IMHO.

Typically, ammo gets you the most bang for the buck as it never runs out and all your soldiers can use them regardless of what armour they're packing.